冷冻食品（英文第二版）：34990wp_13

13.1 Introduction The primary concern of chilled food manufacturers is to produce a product that is both wholesome, i.e. it has all the fresh, quality attributes associated with a chilled food, and safe, i.e. free from pathogenic microorganisms and chemical and foreign body contamination. This is particularly important in this product sector as, due to the nature and method of production, many chilled foods are classified as high-risk products. The schematic diagram shown in Fig. 13.1, which is typical for all food factories, shows that the production of safe, wholesome foods stems from a thorough risk analysis. Indeed this is now a legal requirement. The diagram also shows that given specified raw materials, there are four major ‘building blocks’ that govern the way the factory is operated to ensure that the safe, wholesome food goal is realised. Hygienic design dictates the design of the production facility and equipment whilst process development enables the design of safe, validated processes. Hygienic practices and process control subsequently ensure the respective integrity of these two dependables. Risk analysis encompasses identifying the hazards that may affect the quality or safety of the food product and controlling them at all stages of the process such that product contamination is minimised. In the food industry this is commonly referred to as Hazard Analysis Critical Control Point (HACCP). Such hazards are usually described as ? biological, e.g. bacteria, yeasts, moulds ? chemical, e.g. cleaning chemicals, lubricating fluids ? physical, e.g. glass, insects, pests, metal, dust. 13 The hygienic design of chilled foods plant J. Holah and R. H. Thorpe, Campden and Chorleywood Food Research Association A hazard analysis should be undertaken at the earliest opportunity in the process of food production and if possible, before the design and construction of the processing facility. This allows the design of the production facility to play a major role in hazard elimination or risk reduction. Of the four building blocks illustrated in Figure 13.1, this chapter deals with hygienic design. For the food factory, hygienic design begins at the level of its siting and construction and is concerned with such factors as the design of the building structure, the selection of surface finishes, the segregation of work areas to control hazards, the flow of raw materials and product, the movement and control of people, the design and installation of the process equipment and the design and installation of services (air, water, steam, electrics, etc.). With regard to legislation, there are some EEC Directives relating to the production of certain foodstuffs, such as meat, fish and egg products, in which requirements for the premises are specified. On the 14 June, 1993, however, a Council Directive on the hygiene of foodstuffs was adopted (Council Directive 93/43/EEC). This Directive applies to the production of all foodstuffs and it is more specific than any previous regulations. The first of ten chapters covers the general requirements for food premises and the second the specific requirements for room where foodstuffs are prepared, treated or processed; only dining areas MT72MT65MT67MT67MT80 MT72MT121MT103MT105MT101MT110MT105MT99MT32MT100MT101MT115MT105MT103MT110 MT80MT114MT111MT99MT101MT115MT115MT32MT100MT101MT118MT101MT108MT111MT112MT109MT101MT110MT116 MT72MT121MT103MT105MT101MT110MT105MT99MT32MT112MT114MT97MT99MT116MT105MT99MT101MT115 MT80MT114MT111MT99MT101MT115MT115MT32MT99MT111MT110MT116MT114MT111MT108 MT83MT97MT102MT101MT32MT119MT104MT111MT108MT101MT115MT111MT109MT101 MT102MT111MT111MT100 MT83MT112MT101MT99MT105MT102MT105MT101MT100MT32MT114MT97MT119 MT109MT97MT116MT101MT114MT105MT97MT108MT115 Fig. 13.1 Schematic stages required to ensure safe, wholesome chilled products. 356 Chilled foods and premises specified in Chapter 3, e.g. marquees, market stalls etc. are excluded. Within all of these documents, however, advice is at best, concise. 13.2 Segregation of work zones Factories should be constructed as a series of barriers that aim to limit the entrance of contaminants. The number of barriers created will be dependent on the nature of the food product and will be established from the HACCP study. Figure 13.2 shows that there are up to three levels of segregation that are typical for food plants. Level 1 represents the siting of the factory, the outer fence and the area up to the factory wall. This level provides barriers against environmental conditions e.g. prevailing wind and surface water run-off, unauthorised public access and avoidance of pest harbourage areas. Level 2 represents the factory wall and other processes (e.g. UV flytraps) which should separate the factory from the external environment. Whilst it is obvious that the factory cannot be a sealed box, the floor of the factory should ideally be at a different level to the ground outside and openings should be designed to be pest proof when not in use. Level 3 represents the internal barriers that are used to separate manufacturing processes of different risk e.g. pre and post-heat treatment. Such separation should seek to control the air, people and surfaces (e.g. the floor and drainage systems) and the passage of materials and utensils across the barrier. Fig. 13.2 Schematic layout of a factory site showing ‘barriers’ against contamination. (1) Perimeter fence; (2) Main factory buildings; (3) Walls of high-care area. The hygienic design of chilled foods plant 357 13.2.1 The factory site Attention to the design, construction and maintenance of the site surrounding the factory provides an opportunity to set up the first (outer) of a series of barriers to protect production operations from contamination. It is a sound principle to take all reasonable precautions to reduce the ‘pressures’ that may build up on each of the barriers making up the overall protective envelope. A number of steps can be taken. For example, well-planned and properly maintained landscaping of the grounds can assist in the control of rodents, insects, and birds by reducing food supplies and breeding and harbourage sites. The use of two lines of rodent baits located every 15–21m along the perimeter boundary fencing and at the foundation walls of the factory, together with a few mouse traps near building entrances is advocated by Imholte (1984). Both Katsuyama and Strachan (1980) and Troller (1983) suggest that the area immediately adjacent to buildings be kept grass free and covered with a deep layer of gravel or stones. This practice helps weed control and assists inspection of bait boxes and traps. The control of birds is important, otherwise colonies can become established and cause serious problems. Shapton and Shapton (1991) state there should be a strategy of making the factory site unattractive by denying birds food and harbourage. They stress the importance of ensuring that waste material is not left in uncovered containers and that any spillages of raw materials are cleared up promptly. Shapton and Shapton (1991) state that many insects are carried by the wind and therefore are inevitably present in a factory. They point out the importance of preventing the unauthorized opening of doors and windows and the siting of protective screens against flying insects. Imholte (1984) considers such screens present maintenance problems. These authors draw attention to lighting for warehouses and outdoor security systems attracting night-flying insects and recommend high pressure sodium lights in preference to mercury vapour lamps. Entrances that have to be lit at night should be lit from a distance with the light directed to the entrance, rather than lit from directly above. This prevents flying insects being attracted directly to the entrance. Some flying insects require water to support part of their life cycle e.g. mosquitoes, and experience has shown that where flying insects can occasionally be a problem, all areas where water could collect or stand for prolonged periods of time (old buckets, tops of drums, etc.) need to be removed or controlled, Good landscaping of sites can reduce the amount of dust blown into the factory, as can the sensible siting of any preliminary cleaning operations for raw materials such as root vegetables, which are often undertaken outside the factory. Imholte (1984) advocates orientating buildings so that prevailing winds do not blow directly into manufacturing areas. The layout of vehicular routes around the factory site can affect the amount of soil blown into buildings. Shapton and Shapton (1991) suggest that for some sites it may be necessary to restrict the routes taken by heavily soiled vehicles to minimize dust contamination. 358 Chilled foods 13.2.2 The factory building The building structure is the second and a major barrier, providing protection for raw materials, processing facilities and manufactured products from contamina- tion or deterioration. Protection is both from the environment, including rain, wind, surface runoff, delivery and dispatch vehicles, dust, odours, pests and uninvited people etc. and internally from microbiological hazards (e.g. raw material cross-contamination), chemical and physical hazards (e.g. from plantrooms and engineering workshops). Ideally, the factory buildings should be designed and constructed to suit the operations carried out in them and should not place constraints on the process or the equipment layout. The type of building, either single- or multistorey, needs to be considered. Imholte (1984), comments that the subject has always been a controversial one and describes the advantages and disadvantages of both types of buildings. He also suggests a compromise may be achieved by having a single-storey building with varying headroom featuring mezzanine floors to allow gravity flow of materials, where this is necessary. Single-storey buildings are preferred for the majority of chilled food operations and generally allow the design criteria for high-risk areas to be more easily accommodated. However, it should be appreciated that where production is undertaken in renovated buildings, it may not be possible to capitalize on some of the advantages quoted by Imholte (1984). Of particular concern in multistorey buildings is leakage, of both air and fluids, from areas above and below food processing areas. The authors have undertaken investigative work in a number of factories in which contamination has entered high-risk areas via leakage from above, through both floor defects and badly maintained drains. In addition, on a number of occasions the drainage systems have been observed to act as air distribution channels, with air from low-risk areas (both above and below) being drawn into high risk. This can typically occur when the drains are little used and the water traps dry out. The factory layout is paramount in ensuring both an economic and safe processing operation and should be such that processing operations are as direct as possible. Straight line flow minimises the possibility of contamination of processed or semi-processed product by unprocessed or raw materials and is more efficient in terms of handling. It is also easier to segregate clean and dirty process operations and restrict movement of personnel from dirty to clean areas. Whilst ideally the process line should be straight, this is rarely possible, but there must be no backtracking and, where there are changes in the direction of process flow, there must be adequate physical barriers. The layout should also consider that provision is made for the space necessary to undertake the process and associated quality control functions, both immediately the factory is commissioned and in the foreseeable future. Space should also be allowed for the storage and movement of materials and personnel. Surrounding equipment, Imholte (1984) states 915 mm (3.0 feet) should be considered as the bare minimum for most units; however, he recommends 1830 mm (6.0 feet) as a more practical figure to allow production, cleaning and maintenance operations to be undertaken in an efficient manner. The hygienic design of chilled foods plant 359 In addition to process areas, provision may have to be made for a wide range of activities including raw material storage; packaging storage; water storage; wash-up facilities; plantroom; engineering workshop; cleaning stores; micro- biology, chemistry and QC laboratories; test kitchens; pilot plant; changing facilities; restrooms; canteens; medical rooms; observation areas/viewing galleries and finished goods dispatch and warehousing. Other good design principles given by Shapton and Shapton (1991) are: ? The flow of air and drainage should be away from ‘clean’ areas towards ‘dirty’ ones. ? The flow of discarded outer packaging materials should not cross, or run counter to, the flow of either unwrapped ingredients or finished products. Detailed information on the hygienic design requirements for the construction of the external walls or envelope of the factory is not easily found. Much of the data available is understandably concerned with engineering specifications, which are not considered in this chapter. Shapton and Shapton (1991), Imholte (1984) and Timperley (1994) discuss the various methods of forming the external walls and give a large amount of advice on pest control measures, particularly for rodents. A typical example of a suitable outside wall structure is shown in Figure 13.3. The diagram shows a well sealed structure that resists pest ingress and is protected from external vehicular damage. The ground floor of the factory is also at a height above the external ground level. By preventing direct access into the factory at ground floor level, the entrance of contamination (mud, soil, foreign bodies etc.), particularly from vehicular traffic (forklift trucks, raw material delivery etc.) is restricted. In addition, the above references provide considerable information on the hygienic requirements for the various openings in the envelope, particularly doors and windows. Points of particular interest are: ? Doors should be constructed of metal, glass reinforced plastic (GRP) or plastic, self-closing, designed to withstand the intended use and misuse and be suitably protected from vehicular damage where applicable. ? Exterior doors should not open directly into production areas and should remain closed when not in use. Plastic strip curtains may be used as inner doors. ? If possible, factories should be designed not to have windows in food processing areas. If this is not possible, e.g. to allow visitor or management observation, windows should be glazed with either polycarbonate or laminated. A glass register, detailing all types of glass used in the factory, and their location, should be composed. ? Metal or plastic frames with internal sills sloped (20oC040o) to prevent their use as ‘temporary’ storage places and with external sills sloped at 60o to prevent bird roosting, should be used. ? Opening windows must be screened in production areas and the screens be designed to withstand misuse or attempts to remove them. 360 Chilled foods 13.2.3. High-risk production area It is unfortunate that the term ‘high risk’, which is also used to describe other foods, for example low-acid canned foods, has become associated with the particular area of the factory where chilled foods are produced. The terms ‘high- risk area’ and ‘low-risk area’ are often used to describe parts of a chilled foods factory where different hygiene requirements apply. It is considered that such terminology is misleading, and its use can imply to employees and other people that lower overall standards are acceptable in those areas where, for example, operations concerned with raw material reception, storage and initial preparation are undertaken. In practice, all operations concerned with food production should be carried out to the highest standard. Unsatisfactory practices in so-called low-risk areas may put greater pressures on the ‘barrier system’ separating the two areas. Whilst undesirable, however, it is probable that such terminology will remain for the near future. The advent of the use of more ‘pharmaceutical’ techniques in hygienic food manufacture may lead to the use of appropriate pharmaceutical terminology, e.g. ‘clean’ zones. Fig. 13.3 Outside wall configuration showing a well sealed structure with elevated factory floor level. The hygienic design of chilled foods plant 361 More recently, the Chilled Food Association in the UK (Anon. 1997a) established guidelines to describe the hygiene status of chilled foods and indicate the area status of where they should be processed after any heat treatment. Three levels were described, high-risk area (HRA), high-care area (HCA) and good manufacturing practice (GMP). Their definitions were: HRA An area to process components, ALL of which have been heat treated to > 90oC for 10 mins or > 70oC for 2 mins, and in which there is a risk of contamination between heat treatment and pack sealing that may present a food safety hazard. HCA An area to process components, SOME of which have been heat treated to > 70oC for 2 mins, and in which there is a risk of contamination between heat treatment and pack sealing that may present a food safety hazard. GMP An area to process components, NONE of which have been heat treated to > 70oC for 2 mins, and in which there is a risk of contamination prior to pack sealing that may present a food safety hazard. In practice, the definition of HCA has been extended to include an area to further process components that have undergone a decontamination treatment e.g. fruit and vegetables after washing in chlorinated water or fish after low temperature smoking and salting. Most of the requirements for the design of HRA and HCA operations are the same, with the emphasis on preventing contamination in HRA and minimising contamination in HCA operations (Anon. 1997a). In considering whether a high risk or high care is required and therefore what specifications should be met, chilled food manufacturers need to carefully consider their existing and future product ranges, the hazards and risks associated with them and possible developments in the near future. If budgets allow, it is always cheaper to build to the highest standards from the onset of construction rather than try to retrofit or refurbish at a later stage. Guidance within this chapter is aimed at satisfying the requirements for high-risk operations. Listeria philosophy In terms of chilled food product safety, the major contamination risk is microbiological, particularly from the pathogen most commonly associated with the potential to grow in chilled foods, Listeria monocytogenes. For many chilled food products, L. monocytogenes could well be associated with the raw materials used and thus may well be found in the low-risk area. After the product has been heat processed or decontaminated (e.g. by washing), it is essential that all measures are taken to protect the product from cross-contamination from low risk, L. monocytogenes sources. Similarly, foreign body contamination that would jeopardize the wholesomeness of the finished product, could also be found in low risk. A three-fold philosophy has been developed by the authors to help reduce the incidence of L. monocytogenes in finished product and at the same time, control other contamination sources. 362 Chilled foods 1. Provide as many barriers as possible to prevent the entry of Listeria into the high-risk area. 2. Prevent the growth and spread of any Listeria penetrating these barriers during production. 3. After production, employ a suitable sanitation system to ensure that all Listeria are removed from high risk prior to production recommencing. 13.3 High-risk barrier technology The building structure, facilities and practices associated with the high-risk production and assembly areas provide the third and inner barrier protecting chilled food manufacturing operations from contamination. This final barrier is built up by the use of combinations of a number of separate components or sub-barriers, to control contamination that could enter high risk from the following routes: ? product entering high risk via a heat process ? product entering high risk via a decontamination process. Product entering high risk that has been heat processed/decontaminated off-site but whose outer packaging may need decontaminating on entry to high risk ? other product transfer ? packaging materials ? liquid and solid waste materials ? surfaces, usually associated with low/high-risk physical junctions and concerned with floors, walls, doors, and false or suspended ceilings ? food operatives entering high risk ? the air ? utensils, which may have to be passed between low and high risk 13.3.1. Heat treated product Where a product heat treatment forms the barrier between low and high risk (e.g. an oven, fryer or microwave tunnel), two points are critical to facilitate its successful operation. 1. All product passing through the heat barrier must receive its desired cooking time/temperature combination. This means that the heating device should be performing correctly (e.g. temperature distribution and maintenance are established and controlled and product size has remained constant) and that it should be impossible, or very difficult, for product to pass through the heat treatment without a cook process being initiated. 2. The heating device must be designed such that as far as is possible, the device forms a solid, physical barrier between low and high risk. Where it is not physically possible to form a solid barrier, air spaces around the heating equipment should be minimised and the low/high-risk floor junction should be fully sealed to the highest possible height. The hygienic design of chilled foods plant 363 The fitting of heating devices that provide heat treatment within the structure of a building presents two main difficulties. Firstly, the devices have to be designed to load product on the low-risk side and unload in high risk. Secondly, the maintenance of good seals between the heating device surfaces, which cycle through expansion and contraction phases, and the barrier structure which has a different thermal expansion, is problematical. Of particular concern are ovens and the authors are aware of the following issues: ? Some ovens have been designed such that they drain into high risk. This is unacceptable for the following reason. It may be possible for pathogens present on the surface of product to be cooked (which is their most likely location if they have been derived from cross-contamination in low risk) to fall to the floor through the melting of the product surface layer (or exudate on overwrapped product) at a temperature that is not lethal to the pathogen. The pathogen could then remain on the floor or in the drain of the oven in such a way that it could survive the cook cycle. On draining, the pathogen would then subsequently drain into high risk. Pathogens have been found at the exit of ovens in a number of food factories. ? Problems have occurred with leakage from sumps under the ovens into high risk. There can also be problems in sump cleaning where the use of high pressure hoses can spread contamination into high risk. ? Where the floor of the oven is cleaned, cleaning should be undertaken in such a way that cleaning solutions do not flow from low to high risk. Ideally, cleaning should be from low risk with the high-risk door closed and sealed. If cleaning solutions have to be drained into high risk, or in the case of ovens that have a raining water cooling system, a drain should be installed immediately outside the door in high risk. Other non-oven related issues to consider include the following: ? The design of small batch product blanchers or noodle cookers (i.e. small vessels with water as the cooking medium) does not often allow the equipment to be sealed into the low/high-risk barrier as room has to be created around the blancher to allow product loading and unloading. Condensation is likely to form because of the open nature of these cooking vessels and it is important to ventilate the area to prevent microbial build-up where water condenses. Any ventilation system should be designed so that the area is ventilated from low risk; ventilation from high risk can draw into high risk large quantities of low-risk air. ? Early installations of kettles as barriers between low and high risk, together with the associated bund walls to prevent water movement across the floor and barriers at waist height to prevent the movement of people, whilst innovative in their time, are now seen as hygiene hazards. It is virtually impossible to prevent the transfer of contamination, by people, the air and via cleaning, between low and high risk. It is now possible to install kettles within low risk and transfer product (by pumping, gravity, vacuum etc.) 364 Chilled foods through into high risk via a pipe in the dividing wall. The kettles need to be positioned in low risk at a height such that the transfer into high risk is well above ground level. Installations have been encountered where receiving vessels have had to be placed onto the floor to accept product transfer. 13.3.2 Product decontamination Fresh produce to be processed in high care should enter high care via a decontamination operation, usually involving a washing process with the washwater incorporating a biocide. The use of chlorinated dips, mechanically stirred washing baths or ‘jaquzzi’ washers are the most common method, though alternative biocides are also used (e.g. bromine, chlorine dioxide, ozone, organic acids, peracetic acid, hydrogen peroxide). In addition, it is now seen as increasingly important, following a suitable risk assessment, to decontaminate the outer packaging of various ingredients on entry into high risk (e.g. product cooked elsewhere and transported to be processed in the high-risk area, canned foods and some overwrapped processed ingredients). Where the outer packaging is likely to be contaminated with food materials, decontamination is best done using a washing process incorporating a disinfectant (usually a quaternary ammonium compound). If the packaging is clean, the use of UV light has the advantage that it is dry and thus limits potential environmental microbial growth. Decontamination systems have to be designed and installed such that they satisfy three major criteria. 1. As with heat barriers, decontamination systems need to be installed within the low/high-risk barrier to minimise the free space around them. As a very minimum, the gap around the decontamination system should be smaller than the product to be decontaminated. This ensures that all ingredients in high risk must have passed through the decontamination system and thus must have been decontaminated (it is impossible to visually assess whether the outer surface of an ingredient has been disinfected, in contrast to whether an ingredient has been heat processed). 2. Prior to installation, the decontamination process should be established and verified. For a wet process, this will involve the determination of a suitable disinfectant that combines detergency and disinfectant properties and a suitable application temperature, concentration and contact time. Similarly, for UV light, a suitable wavelength, intensity and contact time should be determined. The same degree of decontamination should apply to all the product surfaces or, if this is not possible, the process should be established for the surface receiving the least treatment. 3. After installation, process controls should be established and may include calibrated, automatic disinfectant dosing, fix speed conveyors, UV light intensity meters etc. In process monitoring may include the periodic checking for critical parameters, for example blocked spray nozzles or UV The hygienic design of chilled foods plant 365 lamp intensity and, from the low-risk side, the loading of the transfer conveyor to ensure that product is physically separated such that all product surfaces are exposed. 13.3.3 Other product transfer It is now poor practice to bring outer packaging materials into high risk. All ingredients and product packaging must, therefore, be de-boxed and transferred into high risk. Some ingredients, such as bulk liquids that have been heat-treated or are inherently stable (e.g. oils or pasteurised dairy products), are best handled by being pumped across the low/high-risk barrier directly to the point of use. Dry, stable bulk ingredients (e.g. sugar) can also be transferred into high risk via sealed conveyors. For non-bulk quantities, it is possible to open ingredients at the low/high-risk barrier and decant them through into high risk via a suitable transfer system (e.g. a simple funnel set into the wall), into a receiving container. Transfer systems should, preferably, be closeable when not in use and should be designed to be cleaned and disinfected, from the high-risk side, prior to use as appropriate. 13.3.4 Packaging Packaging materials (film reels, cartons, containers, trays etc.) are best supplied to site ‘double bagged’. This involves a cardboard outer followed by two plastic bag layers surrounding the packaging materials. The packaging is brought on site, de-boxed, and stored double bagged until use in a suitable packaging store. When called for in high risk, the packaging material is brought to the low/high- risk barrier, the outer plastic bag removed and the inner bag and packaging enters high risk through a suitable hatch. The second plastic bag keeps the packaging materials covered until they are loaded onto the line or the packaging machine. The hatch, as with all openings in the low/high-risk barrier, should be as small as possible and should be closeable when not in use. This is to reduce airflow through the hatch and thus reduce the airflow requirements for the air handling systems to maintain high-risk positive pressure. For some packaging materials, especially heavy film reels, it may be required to use a conveyor system for moving materials through the hatch. An opening door or preferably, double door airlock, should only be used if the use of a hatch is not technically possible and suitable precautions must be taken to decontaminate the airlock after use. 13.3.5 Liquid and solid wastes On no account should low-risk liquid or solid wastes be removed from the factory via high risk and attention is required to the procedures for removing high-risk wastes. The handling of liquid wastes from low and high risk is described later in this chapter in the section on drainage. 366 Chilled foods Solid wastes that have fallen on the floor or equipment, etc., through normal production spillages, should be bagged-up or placed in easily cleanable bins, on an on-going basis commensurate with good housekeeping practices. It may also be necessary to remove solid waste product from the line at break periods or to facilitate line product changes. Waste bags should leave high risk in such a way that they minimise any potential cross-contamination with processed product and should, preferably, not be routed in the reverse direction to the product. For small quantities of bagged waste, existing hatches should be used e.g. the wrapped product exit hatches or the packaging materials entrance hatch, as additional hatches increase the risk of external contamination and put extra demands on the air handling system. For waste collected in bins, it may be necessary to decant the waste through purpose built, easily cleanable from high risk, waste chutes that deposit directly into waste skips. Waste bins should be colour coded to differentiate them from other food containers and should only be used for waste. 13.3.6 Surfaces In this context, surfaces are associated with sealed low/high-risk physical junctions and are concerned with floors, walls, doors and false or suspended ceilings. Detailed descriptions on the requirements for these areas are contained in the Construction section later in this chapter. 13.3.7 Personnel Within the factory building, provision must be made for adequate and suitable staff facilities and amenities for changing, washing and eating. There should be lockers for storing outdoor clothing in areas that must be separate from those for storing work clothes. Toilets must be provided and must not open directly into food-processing areas, all entrances of which must be provided with handwashing facilities arranged in such a way that their ease of use is maximised. In addition, staff (including visitors and contractors etc.) have personal responsibilities which they should follow to ensure good hygienic practices. These are normally formulated as the factory hygiene policy and typically include the following: 1. Protective clothing, footwear and headgear issued by the company must be worn and must be changed regularly. When considered appropriate by management, a fine hairnet must be worn in addition to the protective headgear provided. Hair clips and grips should not be worn. 2. Protective clothing must not be worn off the site and must be kept in good condition. 3. Beards must be kept short and trimmed and a protective cover worn when considered appropriate by management. 4. Nail varnish, false nails and make up must not be worn in production areas. The hygienic design of chilled foods plant 367 5. False eyelashes, wrist watches and jewellery (except wedding rings, or the national equivalent, and sleeper earrings) must not be worn. 6. Hands must be washed regularly and kept clean at all times. 7. Personal items must not be taken into production areas unless carried in inside overall pockets (handbags, shopping bags, etc. must be left in the lockers provided). 8. Food and drink must not be taken into or consumed in areas other than the rest areas and the staff canteen/restaurant. 9. Sweets and chewing gum must not be consumed in production areas. 10. Smoking or taking snuff is forbidden in food production, warehouse and distribution areas where ‘No Smoking’ notices are displayed. 11. Spitting is forbidden in all areas on the site. 12. Superficial injuries (e.g. cuts, grazes, boils, sores and skin infections) must be reported to the medical department or the first aider on duty via the line supervisor and clearance obtained before the operative can enter production areas. 13. Dressings must be waterproof, suitably coloured to differentiate them from product and contain a metal strip as approved by the medical department. 14. Infectious diseases (including stomach disorders, diarrhoea, skin conditions and discharge from eyes, nose or ears) must be reported to the medical department or first aider on duty via the line supervisor. This also applies to staff returning from foreign travel where there has been a risk of infection. 15. All staff must report to the medical department when returning from both certified and uncertified sickness. With regard to high-risk operatives, however, personnel facilities and requirements must be provided in a way that minimises any potential con- tamination of high-risk operations. The primary sources of potential contamina- tion arise from the operatives themselves and from low-risk operations. This necessitates further attention to protective clothing and, in particular, special arrangements and facilities for changing into high-risk clothing and entering high risk. Best practice with respect to personnel hygiene is continually developing and has been recently reviewed by Guzewich and Ross (1999), Taylor and Holah (2000) and Taylor et al. (2000). High-risk factory clothing does not necessarily vary from that used in low risk in terms of style or quality, though it may have received higher standards of laundry, especially related to a higher temperature process, sufficient to significantly reduce microbiological levels. Indeed some laundries now operate to the same low/high-risk principles as the food industry such that dirty laundry enters ‘low risk’, is loaded into a washing machine that bridges a physical divide, is cleaned and disinfected and exits into ‘high risk’ to be dried and packed. Additional clothing may be worn in high risk, however, to further protect the food being processed from contamination arising from the operatives body (e.g. gloves, sleeves, masks, whole head coveralls, coats with hoods, boiler suits, etc.). All clothing and footwear used in the high-risk area is colour coded to 368 Chilled foods distinguish it from that worn in other parts of the factory and to reduce the chance that a breach in the systems would escape early detection. High-risk footwear should be captive to high risk; i.e. it should remain within high risk, operatives changing into and out of footwear at the low/high-risk boundary. This has arisen because research has shown that boot baths and boot washers are unable adequately to disinfect low-risk footwear such that they can be worn in both low and high risk and decontaminated between the two (Taylor et al. 2000). In addition, boot baths and boot washers can both spread contamination via aerosols and water droplets that, in turn, can provide moisture for microbial growth on high-risk floors. Bootwashers were, however, shown to be very good at removing organic material from boots and are thus a useful tool in low-risk areas both to clean boots and help prevent operative slip hazards. The high-risk changing room provides the only entry and exit point for personnel working in or visiting the area and is designed and built to both house the necessary activities for personnel hygiene practices and minimise contamination from low risk. In practice, there are some variations in the layout of facilities of high-risk changing rooms. This is influenced by, for example, space availability, product throughput and type of products, which will affect the number of personnel to be accommodated and whether the changing room is a barrier between low- and high-risk operatives or between operatives arriving from outside the factory and high risk. Generally higher construction standards are required for low/high-risk barriers than outside/high-risk barriers because the level of potential contamination in low risk, both on the operatives hands and in the environment, is likely to be higher (Taylor and Holah 2000). In each case, the company must evaluate the effectiveness of the changing-room layout and procedure to ensure the high-risk area and products prepared in it are not being put at risk. This is best undertaken by a HACCP approach, so that data are obtained to support or refute any proposals regarding the layout or sequence. Research at CCFRA has also proposed the following hand hygiene sequence to be used on entry to high risk (Taylor and Holah 2000). This sequence has been designed to maximise hand cleanliness, minimise hand transient microbiological levels, maximise hand dryness yet at the same time reduce excessive contact with water and chemicals that may both lead to dermatitis issues of the operatives and reduce the potential for water transfer into high risk. 1. Remove low-risk or outside clothing. 2. Remove low-risk/outside footwear and place in designated ‘cage’ type compartment. 3. Cross over the low- risk/high-risk dividing barrier. 4. WASH HANDS. 5. Put on in the following order: ? high-risk captive footwear ? hair net; put on over ears and covering all hair; (plus beard snood if needed) and hat (if appropriate) ? overall (completely buttoned up to neck). The hygienic design of chilled foods plant 369 Fig. 13.4 Schematic layout for a high-risk changing room. 6. Check dress and appearance in the mirror provided. 7. Go into the high-risk production area and apply an alcohol-based sanitizer. 8. Draw and put on disposable gloves, sleeves and apron, if appropriate. A basic layout for a changing room is shown in Fig. 13.4 and has been designed to accommodate the above hand hygiene procedure and the following requirements. ? An area at the entrance to store outside or low-risk clothing. Lockers should have sloping tops. ? A barrier to divide low- and high-risk floors. This is a physical barrier such as a small wall (approximately 60cm high), that allows floors to be cleaned on either side of the barrier without contamination by splashing, etc. between the two. ? Open lockers at the barrier to store low-risk footwear. ? A stand on which footwear is displayed/dried. ? An area designed with suitable drainage for bootwashing operations. Research has shown (Taylor et al. 2000) that manual cleaning (preferably during the cleaning shift) and industrial washing machines are satisfactory bootwashing methods. ? Hand wash basins to service a single, hand wash. Handwash basins must have automatic or knee/foot operated water supplies, water supplied at a suitable temperature (that encourages hand washing) and a waste extraction system piped directly to drain. It has been shown that hand wash basins positioned at the entrance to high risk, which was the original high-risk design concept to allow visual monitoring of hand wash compliance, gives rise to substantial aerosols of Staphylococcal strains that can potentially contaminate the product. ? Suitable hand-drying equipment e.g. paper towel dispensers or hot-air dryers and, for paper towels, suitable towel disposal containers. ? Access for clean factory clothing and storage of soiled clothing. For larger operations this may be via an adjoining laundry room with interconnecting hatches. ? Interlocked doors are possible such that doors only allow entrance to high risk if a key stage, e.g. hand washing has been undertaken. ? CCT cameras as a potential monitor of hand wash compliance. ? Alcoholic hand rub dispensers immediately inside the high-risk production area. There may be the requirement to site additional hand washbasins inside the high- risk area if the production process is such that frequent hand washing is necessary. As an alternative to this, Taylor et al. (2000) demonstrated that cleaning hands with alcoholic wipes, which can be done locally at the operative’s work station, is an effective means of hand hygiene. 13.3.8 Air The air is an important, potential source of pathogens and the intake into the high-risk area has to be controlled. Air can enter high risk via a purpose-built The hygienic design of chilled foods plant 371 air-handling system or can enter into the area from external uncontrolled sources (e.g. low-risk production, packing, outside). For high-risk areas, the goal of the air-handling system is to supply suitably filtered fresh air, at the correct temperature and humidity, at a slight overpressure to prevent the ingress of external air sources. The cost of the air-handling systems is one of the major costs associated with the construction of a high-risk area and specialist advice should always be sought before embarking on an air-handling design and construction project. Following a suitable risk analysis, it may be concluded that the air-handling requirements for high-care areas may be less stringent, especially related to filtration levels and degree of overpressure. Once installed, any changes to the construction of the high-risk area (e.g. the rearrangement of walls, doors or openings) should be carefully considered as they will have a major impact on the air-handling system. Air quality standards for the food industry were reviewed by a CCFRA Working Party and guidelines were produced (Brown 1996). The design of the air-handling system should consider the following issues: ? degree of filtration of external air ? overpressure ? air flow – concerned with operational considerations and operative comfort ? air movement ? temperature requirements ? local cooling and barrier control ? humidity requirements ? installation and maintenance. The main air flows within a high-risk area are shown in Fig. 13.5 and a more detailed schematic of the air handling system is shown in Fig. 13.6. A major risk of airborne contamination entering high risk is from low-risk processing operations, especially those handling raw produce that is likely to be contaminated with pathogens. The principal role of the air-handling system is thus to provide filtered air to high risk with a positive pressure with respect to low risk. This means that wherever there is a physical break in the low/high-risk barrier, e.g. a hatch, the air flow will be through the opening from high to low risk. Microbial airborne levels in low risk, depending on the product and processes being undertaken, may be quite high (Holah et al. 1995) and overpressure should prevent the movement of such airborne particles, some of which may contain viable pathogenic microorganisms, entering high risk. To aid the performance of the air-handling system, it is also important to control potential sources of aerosols, generated from personnel, production and cleaning activities, in both low and high risk. Filtration of air is a complex matter and requires a thorough understanding of filter types and installations. The choice of filter will be dictated by the degree of microbial and particle removal required and filter types are described in detail in the CCFRA guideline document (Brown 1996). For high-risk applications, a series of filters is required 372 Chilled foods Fig. 13.5 Schematic diagram showing the airflows within a high-risk or high-care production area. Fig 13.6 Schematic diagram of the components of a typical air-handling system. (Fig. 13.6) to provide air to the desired standard and is usually made up of a G4/ F5 panel or pocket filter followed by an F9 rigid cell filter. For some high-risk operations an H10 or H11 final filter may be desirable, whilst for high-care operations an F7 or F8 final filter may be acceptable. To be effective, the pressure differential between low and high risk should be between 5–15 Pascals. The desired pressure differential will be determined by both the number and size of openings and also the temperature differentials between low and high risk. For example if the low-risk area is at ambient (20oC) and the high-risk areas at 10oC, hot air from low risk will tend to rise through the opening whilst cold air from high risk will tend to sink through the same opening, causing two-way flow. The velocity of air through the opening from high risk may need to be 1.5m/sec or greater to ensure one-way flow is maintained. In addition to providing a positive over-pressure, the air-flow rate must be sufficient to remove the heat load imposed by the processing environment (processes and people) and provide operatives with fresh air. Generally 5–25 air changes per hour are adequate, though in a high-risk area with large hatches/ doors that are frequently opened, up to 40 air changes per hour may be required. Air is usually supplied to high risk by either ceiling grilles or textile ducts (socks), usually made from polyester or polypropylene to reduce shrinkage. Ceiling grilles have the advantage that they are cheap and require little maintenance but have limitations on velocity and flow rate without high noise levels or the potential to cause draughts. With respect to draughts, the maximum air speed close to workers to minimise discomfort through ‘wind-chill’ is 0.3m s C01 . Air socks have the ability to distribute air, at a low draught free velocity with minimal ductwork connections, though they require periodic laundering and spare sets are required. Ceiling mounted chillers that cool and recirculate the air are only really suitable for high-care operations unless additional air supplies are used to maintain positive pressures. Joint work undertaken since 1995 by CCFRA and the Silsoe Research Institute, sponsored by the UK Ministry of Fisheries and Food (MAFF), has looked at the control of airborne microbial contamination in high-risk food production areas. The work has resulted in the production of a best practice guideline on air flows in high-risk areas, which will be published by MAFF in 2001. The work has centred on the measurement of both air flows and airborne microbiological levels in actual food factories and computational fluid dynamics (CFD) models have been developed by Silsoe to predict air and particle (including microorganism) movements. The work has led to innovations in two key areas. Firstly, the influence on airflows of air intakes and air extracts, secondary ventilation systems in, e.g., washroom areas, the number of hatches and doors and their degree of openings and closings, can readily be visualised by CFD. This has led to the redesign of high-risk areas, from the computer screen, such that airflow balances and positive pressures have been achieved. Secondly, the CFD models allow the prediction of the movement of airborne microorganisms The hygienic design of chilled foods plant 375 from known sources of microbial contamination, e.g., operatives. This has allowed the design of air-handling systems which provide directional air that moves particles away from the source of contamination, in a direction that does not compromise product safety. As an illustration, Fig. 13.7 (a) shows the predicted air flows in a real factory generated using a CFD software package developed by Silsoe following air flow measurements. The model was then used to predict the movement of 10C22m particles (similar to shed skin squams) from line operatives (Fig. 13.7 (b)). The predicted tracks indicate that in some cases the airflow is good and moves shed particles away from the product whilst in other cases, particles move directly over or along the product conveyors, thus presenting a hygiene risk. Chilled-foods manufacturers have traditionally chosen to operate their high- risk areas at low temperatures, typically around 10C012oC, both to restrict the general growth of microorganims in the environment and to prevent the growth of some (e.g. Salmonella) but not all (e.g. Listeria) food pathogens. Chilling the area to this temperature is also beneficial in reducing the heat uptake by the product and thus maintaining the chill chain. Moreover, chilled food manufacturers have to ensure that their products meet, in the UK, the requirements of the Food Safety (Temperature Control) Regulations 1995 (Anon. 1995) as well as those imposed by their retail customers. In the UK, The Workplace (Health, Safety and Welfare) Regulations (Anon. 1992a) require that the ‘temperature in all workplaces inside buildings shall be reasonable’, which, in the supporting Approved Code of Practice (1992b), is normally taken to be at least 16oC or at least 13oC where much of the work involves serious physical effort. To help solve this conflict of product and operative temperature, a Working Group comprising members of the Health and Safety Executive (HSE) and the chilled food industry was established at CCFRA in 1996. The Working Group produced a document Guidance on achieving reasonable working temperatures and conditions during production of chilled foods (Brown 2000) which extends the information provided in HSE Food Sheet No. 3 (Rev) Workroom temperatures in places where food is handled (Anon. 1999). The guidance document (Brown 2000) states that employers will first need to consider alternative ways of controlling product temperatures to satisfy the Food Safety (Temperature Control) Regulations (Anon. 1995) rather than simply adopting lower workroom temperatures. If the alternative measures are not practical then it may be justified for hygiene reasons for workrooms to be maintained at temperatures lower than 16oC (or 13oC). Where such lower temperatures are adopted, employers should be able to demonstrate that they have taken appropriate measures to ensure the thermal comfort of employees. Full guidance on these issues is given in the document. Another joint CCFRA/Silsoe, MAFF sponsored project, has examined the use of localised cooling with the objectives of: ? Providing highly filtered (H11-12), chilled air directly over or surrounding product. This could reduce the requirement to chill the whole of the high-risk 376 Chilled foods Fig 13.7 Schematic diagram of: (a) predicted airflows in an actual chilled food factory estalished from airflow measurements. The length and size of the arrow indicates air speed whilst the orientation shows flow direction; (b) predicted flow from line operatives. The flow of product down the five lines is in the direction Y to Z. (Courtesy of Silsoe Research Institute) The hygienic design of chilled foods plant 377 area to 10oC (13oC would be acceptable), and reduce the degree of filtration required (down to H8-9). The requirement for positive pressure in low risk is paramount, however, and the number of air changes per hour would remain unchanged. ? Using the flow of the air to produce a barrier that resists the penetration of aerosol particles, some of which would contain viable microorganisms An example of such a technology is shown in Fig. 13.8 which shows a schematic diagram of a conveyor that has chilled, filtered air directed over it, sufficient to maintain the low temperature of the product. When a microbial aerosol was generated around the operational conveyor, microbiological air sampling demonstrated a 1–2 log reduction of microorganisms within the protected zone. This work has been reported in Burfoot et al. 2000. Fig. 13.8 Schematic diagram of (a) a conveyor belt with cooled, filtered air directed across the product and (b) the reduction in microbial counts (colony forming units, cfu) within the conveyor during operation. The diameter of the circles is directly proportional to the number of cfus recorded. (Courtesy of Silsoe Research Institute) 378 Chilled foods The choice of relative air humidity is a compromise between operative comfort, product quality and environmental drying. A relative humidity of 55– 65% is very good for restricting microbial growth in the environment and increases the rate of equipment and environment drying after cleaning operations. Low humidities can, however, cause drying of the product with associated weight and quality loss, especially at higher air velocities. Higher humidities maintain product quality but may give rise to drying and condensation problems that increase the opportunity for microbial survival and growth. A compromise target humidity of 60–70% is often recommended, which is also optimal for operative comfort. Finally, air-handling systems should be properly installed such that they can be easily serviced and cleaned and as part of the commissioning programme, their performance should be validated for normal use. The ability of the system to perform in other roles should also be established. These could include dumping air directly to waste during cleaning operations, to prevent air contaminated with potentially corrosive cleaning chemicals entering the air handling unit, and recirculating ambient or heated air after cleaning operations to increase environmental drying. 13.3.9 Utensils Wherever possible, any equipment, utensils and tools, etc. used routinely within high risk, should remain in high risk. This may mean that requirements are made for the provision of storage areas or areas in which utensils can be maintained or cleaned. Typical examples include: ? The requirement for ingredient or product transfer containers (trays, bins, etc.) should be minimised but where these are unavoidable they should remain within high risk and be cleaned and disinfected in a separate wash room area. ? Similarly, any utensils (e.g. stirrers, spoons, ladles) or other non-fixed equipment (e.g. depositors or hoppers) used for the processing of the product should remain in high risk and be cleaned and disinfected in a separate washroom area. ? A separate washroom area should be created in which all within-production wet cleaning operations can be undertaken. The room should preferably be sited on an outside wall that facilitates air extraction and air make-up. An outside wall also allows external bulk storage of cleaning chemicals that can be directly dosed through the wall into the ring main system. The room should have its own drainage system that, in very wet operations, may include barrier drains at the entrance and exit to prevent water spread from the area. The wash area should consist of a holding area for equipment, etc. awaiting cleaning, a cleaning area for manual or automatic cleaning (e.g. traywash) as appropriate, and a holding/drying area where equipment can be stored prior to use. These areas should as segregated as possible. The hygienic design of chilled foods plant 379 ? All cleaning equipment, including hand tools (brushes, squeegees, shovels, etc.) and larger equipment (pressure washers, floor scrubbers and automats, etc.) should remain in high risk and be colour coded to differentiate between high- and low-risk equipment if necessary. Special provision should be made for the storage of such equipment when not in use. ? Cleaning chemicals should preferably be piped into high risk via a ring main (which should be separate from the low-risk ring main). If this is not possible, cleaning chemicals should be stored in a purpose built area. ? The most commonly used equipment service items and spares, etc., together with the necessary hand tools to undertake the service, should be stored in high risk. For certain operations, e.g. blade sharpening for meat slicers, specific engineering rooms may need to be constructed. ? Provision should be made in high risk for the storage of utensils that are used on an irregular basis but that are too large to pass through the low/high-risk barrier, e.g. stepladders for changing the air distribution socks. ? Written procedures should be prepared detailing how and where items that cannot be stored in high risk but are occasionally used there, or new pieces of equipment entering high risk, will be decontaminated. If appropriate, these procedures may also need to detail the decontamination of the surrounding area in which the equipment decontamination took place. 13.4 Hygienic construction 13.4.1 Basic design concepts The design of any food-processing area must allow for the accommodation of five basic requirements, i.e. 1. raw materials and ingredients 2. processing equipment 3. staff concerned with the operation of such equipment 4 packaging materials 5. finished products. There is a philosophy which has considerable support, that states that all other requirements should be considered as secondary to these five basic requirements and, wherever possible, must be kept out of the processing area. These secondary requirements are: ? structural steel framework of the factory ? service pipework for water, steam and compressed air; electrical conduits and trunking; artificial lighting units; and ventilation ducts ? compressors, refrigeration units and pumps ? maintenance personnel associated with any of these services. This philosophy is well suited to the requirements for high-risk production areas. Ashford (1986) describes it as the principle of building a ‘box within a box’ by 380 Chilled foods creating insulated clean rooms within the structural box of the factory with the services and control equipment located in the roof void above the ceiling. Refrigeration equipment and ductwork is suspended from the structural frames and access to all services is provided by catwalks, as shown diagrammatically in Fig. 13.9. This arrangement, if properly undertaken, eliminates a major source of contamination from the process area. 13.4.2 Floors The floor may be considered as one of the most important parts of a building because it forms the basis of the entire processing operation. It is thus worthy of special consideration and high initial capital investment. Guidelines for the design and construction of floors have been prepared by Timperley (1993). Unsatisfactory floors increase the chances of accidents, cause difficulties in attaining the required hygiene standards and put up sanitation costs. The failure of a floor can result in lengthy disruptions of production and financial loss whilst repairs are completed. Many problems with floors have arisen because insufficient attention to detail was taken, at the design stage, with the overall specification. This should cover requirements for: ? the structural floor slab ? the waterproof membrane, which should extend up walls to a height above the normal spillage level ? movement joints in the subfloor and final flooring, around the perimeter of the floor, over supporting walls, around columns and machinery plinths ? drainage, taking into account the proposed layout of equipment Fig. 13.9 Basic design concepts – the separation of production from services and maintenance operations. The hygienic design of chilled foods plant 381 ? screeds, either to give a flat enough surface to accept the flooring or to form the necessary falls when these are not incorporated in the concrete slab ? floor finish, either tiles or a synthetic resin ? processing considerations including trucking; impact loads from proposed operations and equipment and machinery to be installed; degree of product spillage and associated potential problems with corrosion, thermal shock, and drainage requirements; types of cleaning chemicals to be used and requirements for slip resistance The choice of flooring surfaces can be broadly grouped into three categories – concretes, fully vitrified ceramic tiles and seamless resin screeds. Concrete flooring, including the high-strength granolitic concrete finishes, whilst being suitable and widely used in other parts of a factory, is not recommended for high-risk production areas. This is because of its ability to absorb water and nutrients and hence allow microbial growth below the surface, where it is extremely difficult to apply effective sanitation programmes. Pressed or extruded ceramic tiles have been used by the food industry for many years and are still extensively used in processing areas. In recent years they have been partially replaced on grounds of cost by the various seamless resin floors now widely available. Provided tiles of a suitable specification (fully vitrified ceramics) are selected and properly laid – an important prerequisite for all types of flooring – they are perfectly suitable for high-risk production areas and will give a long-life floor available in a very wide choice of colours. Tiles are laid on sand and cement mortar-bonded to the subfloor (thin bed), or on a semi-dry sand and cement mix (thick bed). A tile thickness of approximately 20 mm will provide adequate strength with either of the bedding methods. Thinner tiles (12 mm) are used for bedding into a resin bed by a vibratory method. Tile surfaces may be smooth, studded or incorporate silicon carbide granules to improve slip resistance. Studded tiles are not recommended because of the greater difficulty of cleaning such surfaces. Ideally, surfaces that offer the greatest ease in cleaning should be used. However, in practice, the requirements for anti-slip conditions cannot be ignored and as a result the final choice should reflect a balance of the relevant factors and the emphasis placed on them. Joints should be grouted as soon as practical, otherwise the joint faces may become contaminated. Cementitious grouts are not considered suitable for hygienic applications and resin grouts are normally used. These should not be applied for at least three days after the tiles have been laid, so that water from the bed can evaporate. Epoxy resins are widely used for grouting but do have limited resistance to very high concentrations of sodium hypochlorite and soften at temperatures above 80oC. Polyester and Furan resins are more resistant to chemical attack. Shapton and Shapton (1991) cite data for the chemical resistance of different resins given by Beauchner and Reinert (1972). The grouting material should fill the joints completely to a depth of at least 12 mm and be finished flush with the tile surface. Thinner joints (1 mm) are achieved 382 Chilled foods when tiles are vibrated into a resin bed. The procedure ensures a flat plane and reduces the possibility of damage to the tile edges in use. One advantage of tile floors that is not always fully appreciated is that sections or local areas of damaged surface can be replaced and colour-matched with relative ease, so that the overall standard and appearance of the floor can be maintained. Resin-based seamless floors offer a good alternative means of attaining a hygienic surface provided they are laid on a sound concrete base. The choice of finish can be made either from various resin-based systems (primarily epoxy or polyurethane) or from polymer-modified cementitious systems. The resin-based systems can be broadly grouped under three headings: ? Heavy duty: heavily filled trowel-applied systems 5–12 mm thick. Such screeds are of high strength and are normally slip-resistant. ? Self-levelling: ‘poured and floated’ systems applied at 2–5 mm thickness. These systems are sometimes more correctly described as ‘self-smoothing’. They generally give smooth glossy surfaces. ? Coatings: usually 0.1–0.5 mm thick. They are not recommended for high-risk or other production areas because of their poor durability. Failures of such floors have been associated with microbial contamination, including Listeria monocytogenes, becoming trapped under loosened areas where the coating has flaked. A further aspect that needs to be considered is whether the proposed floor meets legislative requirements. Statements in UK and EC legislation are of a general nature but do call for floors to be ‘waterproof’ or ‘impervious’ and ‘cleanable’. Work at CCFRA (Taylor and Holah 1996) has developed a simple technique to assess the water absorption of flooring materials and materials can be quickly accepted or rejected on any water uptake recorded. Water uptake is unacceptable because if fluids are able to penetrate into flooring materials, microorganisms can be transported to harbourage sites that are impossible to chemically clean and disinfect. Cleanability is more difficult to interpret but both Taylor and Holah (1996) and Mettler and Carpentier (1998) have proposed suitable test methods in which the cleanability of attached microorganisms are assessed. Differences in cleanability between materials have been found but these do not necessarily correlate to surface roughness, traditionally measured as C22mRa. Both sets of authors have shown that microbial cleanability is defined at a magnitude of surface imperfection 100–1000-fold below that as recognized as being important in terms of slip resistance. For example, flooring materials designed to be slip resistant may have an average peak to valley height measured in millimetres, whilst the size of imperfection that could harbour microorganisms would be measured in microns. It is possible, therefore, to obtain ‘rough’ surfaces that are good for slip resistance but, at a micron level, are also good for microbial cleanability and vice versa ‘smooth’ surfaces with limited slip resistance and also poor cleanability at the micron level. When considering the selection of flooring materials, therefore, evidence for imperviousness and cleanability The hygienic design of chilled foods plant 383 should be sought. The floor should be coved where it meets walls or other vertical surfaces such as plinths or columns as this facilitates cleaning. With the considerable choice of resin materials/systems available it is clearly important that the processor reviews the end-user requirements carefully and discusses them in detail with the flooring contractor. Imholte (1984), states that, in general, the higher-quality materials may be more expensive but last longer and have lower maintenance costs. The use of established flooring contractors and the viewing of an existing floor of the type under consideration would also seem to be sensible steps in the selection process. 13.4.3 Drainage Ashford (1986) states that drainage is often neglected and badly constructed. Detailed consideration of the drainage requirements is an important aspect of floor design. Ideally, the layout and siting of production equipment should be finalised before the floor is designed to ensure that discharges can be fed directly into drains. In practice, this is not always possible, and in the food industry in particular, there is a greater chance that the layout of lines will be frequently changed. Equipment should not be located directly over drainage channels as this may restrict access for cleaning. Discharges from equipment, however, should be fed directly into drains to avoid floor flooding. Alternatively, a low wall may be built around the equipment from which water and solids may be drained. Where the channels are close to a wall they should not be directly against it to avoid flooding of the wall to floor junction. An indirect advantage of channels near a wall is that the siting of equipment hard up to the wall is prevented, thus providing access for cleaning. Satisfactory drainage can be achieved only if adequate falls to drainage points are provided. A number of factors should be taken into consideration when establishing the optimum or practical fall, for example: ? Volume of water: wet processes require a greater fall. ? Floor finish: trowelled resin surface finishes require a greater fall than self- levelling ones. Otherwise ‘puddles’ created by small depressions in the surface may remain. ? Safety: falls greater than 1 in 40 may introduce operator safety hazards and also cause problems with wheeled vehicles. Timperley (1993) states that floors should have a fall to drain of between 1 in 50 and 1 in 100, depending upon the process operation and surface texture whilst Cattell (1988), suggests a compromise figure of 1 in 80 for general purposes and safety. The type of drain used depends to a great extent upon the process operation involved. For operations involving a considerable amount of water and solids, channel drains are often the most suitable (Fig. 13.10). For operations generating volumes of water but with little solids, aperture channel drains are more 384 Chilled foods favourable (Fig. 13.10). Many chilled food operations, however, do not require extensive high-volume drainage systems and, in fact, fewer drains lead to less water use and thus increased control of environmental microbial contamination. In such cases, a small number of gulley type drains within the processing area is appropriate. In most cases, channels should have a fall of at least 1 in 100, have round bottoms and be no deeper than 150 mm for ease of cleaning and must be provided with gratings for safety reasons. The channel gratings must be easily removable, with wide apertures (20 mm minimum) to allow solids to enter the drain. In recent years there has been a marked increase in the use of corrosion- resistant materials of construction, such as stainless steel for drain gratings. Stainless steel is also finding a wider use in other drain fittings, e.g. various Fig. 13.10 Half-round drainage channel with reinforced rebate for grating and stainless steel aperture channel drain. The hygienic design of chilled foods plant 385 designs of traps, and for the channels of shallower (low-volume) drainage systems. The profile of aperture channel drains is such that all internal surfaces can be easily cleaned. The edge of the channel rebate must be properly designed and constructed to protect it, by an angle, from damage (Fig. 13.10). This is particularly so if wheeled vehicles are in use, to prevent damage to the channel/floor interface. This is critical in terms of the control of microbial pathogens and the authors are aware of a number of cases where the seal has been broken between the drain channel and floor structure so as to leave an uncleanable void between the two. When the channel is subsequently walked upon or traversed by wheeled vehicles, a small volume of foul liquid and microorganisms is ‘pumped’ to the floor surface. The drainage system should flow in the reverse direction of production (i.e. from high to low risk) and whenever possible, backflow from low-risk to high- risk areas should be impossible. This is best achieved by having separate low- and high-risk drains running to a master collection drain with an air-break between each collector and master drain. The drainage system should also be designed such that rodding points are outside high risk areas. Solids must be separated from liquids as soon as possible, by screening, to avoid leaching and subsequent high effluent concentrations. Traps should be easily accessible, frequently emptied and preferably outside the processing area. 13.4.4 Walls Guidelines for the design and construction of walls, ceilings and services have been prepared by Timperley (1994). A number of different types of materials may be used to construct walls forming the boundaries of a high-risk area and of the individual rooms within the area. When considering the alternative systems, a number of technical factors such as hygiene characteristics, insulation properties, and structural characteristics need to be taken into consideration. Modular insulated panels are now used very widely for non-load-bearing walls. The panels are made of a core of insulating material between 50 and 200 mm thick, sandwiched between steel sheets, which are bonded to both sides of the core. Careful consideration must be given, not only to the fire retardation of the wall insulation or coating material, but also to the toxicity of the fumes emitted in the event of a fire as these could hamper a fire-fighting operation. The steel cladding is generally slightly ribbed to provide greater rigidity and can be finished with a variety of hygienic surface coatings, ready for use. The modules are designed to lock together and allow a silicone sealant to provide a hygienic seal between the units. The modules can be mounted either directly (in a U- shaped channel) onto the floor or on a concrete upstand or plinth (Fig. 13.11). The latter provides useful protection against the possibility of damage from vehicular traffic, particularly fork-lift trucks. However, it should be appreciated that this arrangement reduces the possibility of relatively easy and inexpensive changes to room layout to meet future production requirements. Sections fixed 386 Chilled foods directly onto the floor must be properly bedded in silicone sealant and coved to provide an easily cleanable and watertight junction. As with wall-to-floor joints, it is also good practice to cove wall-to-ceiling junctions to assist cleaning. To ensure continuity in the appearance and surface characteristics of walling throughout a high-risk area, thin sections (50 mm) of insulated panel are sometimes used to cover external or load-bearing walls. When such a practice is adopted, there is a possibility of introducing harbourage sites for pests between the two walling materials. The chances of problems occurring are greatly increased if openings for services are made in the insulated panels without effective sealing. In the UK, load-bearing and fire-break walls are often constructed from brick or blockwork. Walls made from such materials do not generally provide a smooth enough surface to allow the direct application of the various types of coatings. A common practice is to render the brickwork with a cement and sand screed to achieve the desired surface smoothness for the coating layer. The walls may be covered by other materials such as tiles or sheets of plastics. The former is preferred, provided each tile is fully bedded and an appropriate resin is used for grouting. In very wet or humid areas, where there is a strong possibility of Fig. 13.11 Modular insulated panel located in U-channel and fixed to a concrete plinth. The hygienic design of chilled foods plant 387 mould growth, the application of a fungicidal coating may be considered; there is evidence that some such coatings remain effective for many years. Hygiene standards for walls as defined in various EC Directives require that they must be constructed of impervious, non-absorbent, washable, non-toxic materials and have smooth crack-free surfaces up to a height appropriate for the operations. For high-risk areas the standard of construction and finish must apply right up to ceiling level. The same hygienic assessment techniques as described for flooring materials are also directly applicable to wall coverings and finishes. Openings in the walls of the high-risk area need to be limited and controlled and openings for product, packaging and personnel have already been considered. In addition: ? Emergency exits; such doors must be fitted with ‘out-only’ operating bars. The doors must remain closed except in the case of an emergency. ? Larger ‘engineering’ doors required for the occasional access of equipment in and out of high risk; these doors must also remain closed and should be sealed when not in use. 13.4.5 Ceilings When considering the basic design concepts for high-risk areas, the idea of using ceilings to separate production and service functions was discussed. In practice this is often achieved by either using suitable load-bearing insulation panels or suspending sections of insulated panels, as used for the internal walls, from the structural frame of the building. The use of such insulated panels meets legislative requirements by providing a surface that is easily cleanable and will not shed particles. It is important to ensure that drops from services passing through the ceiling are sealed properly to prevent ingress of contamination. Cables may be run in trunking or conduit but this must be effectively sealed against the ingress of vermin and water. All switchgear and controls, other than emergency stop buttons, should, whenever possible, be sited in separate rooms away from processing areas, particularly if wet operations are taking place. Lighting may be a combination of both natural and artificial. Artificial lighting has many advantages in that, if properly arranged, it provides even illumination over inspection belts and a minimum of 500–600 lux is recommended. Fluorescent tubes and lamps must be protected by shields, usually of polycarbonate, to protect the glass and contain it in the event of breakage. Suspended units should be smooth, easily cleanable and designed to the appropriate standards to prevent the ingress of water. It is suggested that lighting units are plugged in so that in the event of a failure the entire unit can be replaced and the faulty one removed from the processing areas to a designated workshop for maintenance. Ideally, recessed lighting flush with the ceiling is recommended from the hygienic aspect (Fig. 13.9) but this is not always possible and maintenance may be difficult. 388 Chilled foods 13.5 Equipment The manufacture of a large proportion of chilled foods generally involves some element of batch or assembly operations or both. The equipment used for such operations is predominantly of the open type, that is, it cannot be cleaned by recirculation (CIP) procedures, and must be of the highest hygienic design standards. Hygienic equipment design provides three major benefits to food manufacturers. 1. Quality – good hygienic design maintains product in the main product flow. This ensures that product is not ‘held-up’ within the equipment where it could deteriorate and affect product quality on rejoining the main product flow. Or, for example in flavourings manufacture, one batch could not taint a subsequent batch. 2. Safety – good hygienic design prevents the contamination of the product with substances that would adversely affect the health of the consumer. Such contamination could be microbiological (e.g. pathogens), chemical (e.g. lubricating fluids, cleaning chemicals) and physical (e.g. glass). 3. Efficiency – good hygienic design reduces the time required for an item of equipment to be cleaned. This reduction of cleaning time is significant over the lifetime of the equipment such that hygienically designed equipment which is initially more expensive (compared to similarly performing poorly designed equipment), will be more cost effective in the long term. In addition, savings in cleaning time may lead to increased production. A relatively few academic texts have been published on hygienic design, though texts by Anon (1983), Timperley and Timperley (1993), the European Hygienic Design Group (EHEDG 1995), Timperley (1997) and Holah (1998) are appropriate to chilled foods. Within Europe (the EHEDG) and the USA (the 3-A Standards and the National Sanitation Foundation – NSF), a number of organisations exist to foster consensus in hygienic design and the use of these organisations’ guidelines can have a quasi-legal status. It should be noted that in Europe, hygienic design guidelines tend to be more generic in nature than the more prescriptive requirements American readers may be familiar with. In the EC, the Council Directive on the approximation of the laws of Member States relating to machinery (89/392/EEC) was published on 14 June 1989. The Directive includes a short section dealing with hygiene and design requirements which states that machinery intended for the preparation and processing of foods must be designed and constructed so as to avoid health risks and consists of seven hygiene rules that must be observed. These are concerned with materials in contact with food; surface smoothness; preference for welding or continuous bonding rather than fastenings; design for cleanability and disinfection; good surface drainage; prevention of dead spaces which cannot be cleaned and design to prevent product contamination by ancillary substances, e.g. lubricants. The Directive requires that all machinery sold within the EC shall meet these basic standards and be marked accordingly to show compliance (the ‘CE’ mark). The hygienic design of chilled foods plant 389 Subsequent to this Directive, a European Standard EN 1672-2 Food processing machinery-Safety and hygiene requirements-Basic concepts-Part 2; Hygiene requirements (Anon. 1997b) has recently been adopted to further clarify the hygiene rules established in 89/392/EEC. In addition to this, a number of specific standards on bakery, meat, catering, edible oils, vending and dispensing, pasta, bulk milk coolers, cereal processing and dairy equipment are in preparation. The basic hygienic design requirements as presented in EN 1672-2 can be summarised under eleven headings and are described below: 1. Construction materials. Materials used for product contact must have adequate strength over a wide temperature range, a reasonable life, be non- tainting, corrosion and abrasion resistant, easily cleaned and capable of being shaped. Stainless steel usually meets all these requirements and there are various grades of stainless steel which are selected for their particular properties to meet operational requirements, e.g. Type 316 which contains molybdenum is used where improved corrosion resistance is necessary. 2. Surface finish. Product contact surfaces must be finished to a degree of surface roughness that is smooth enough to enable them to be easily cleaned. Surfaces will deteriorate with age and wear (abrasion) such that cleaning will become more difficult. 3. Joints. Permanent joints, such as those which are welded, should be smooth and continuous. Dismountable joints, such as screwed pipe couplings must be crevice-free and provide a smooth continuous surface on the product side. Flanged joints must be located with each other and be sealed with a gasket because, although metal/metal joints can be made leak tight, they may still permit the ingress of microorganisms. 4. Fasteners. Exposed screw threads, nuts, bolts, screws and rivets (Fig. 13.12) must be avoided wherever possible in product contact areas. Alternative methods of fastening can be used (Fig. 13.13) where the washer used has a rubber compressible insert to form a bacteria-tight seal. 5. Drainage. All pipelines and equipment surfaces should be self draining because residual liquids can lead to microbial growth or, in the case of cleaning fluids, result in contamination of product. 6. Internal angles and corners. These should be well radiused, wherever possible, to facilitate cleaning. 7. Dead spaces. As well as ensuring that there are no dead spaces in the design of equipment, care must be taken that they are not introduced during installation. 8. Bearings and shaft seals. Bearings should, wherever possible, be mounted outside the product area to avoid possible contamination of product by lubricants, unless they are edible, or possible failure of the bearings due to the ingress of the product. Shaft seals must be of such design so as to be easily cleaned and if not product lubricated, then the lubricant must be edible. Where a bearing is within the product area, such as a foot bearing 390 Chilled foods for an agitator shaft in a vessel, it is important that there is a groove completely through the bore of the bush, from top to bottom to permit the passage of cleaning fluid. 9. Instrumentation. Instruments must be constructed from appropriate materials and if they contain a transmitting fluid, such as in a bourdon tube pressure gauge, then the fluid must be approved for food contact. Many instruments themselves are hygienic but often they are installed unhygienically. 10. Doors, covers and panels. Doors, covers and panels should be designed so that they prevent the entry of and/or prevent the accumulation of soil. Where appropriate they should be sloped to an outside edge and should be easily removed to facilitate cleaning. 11. Controls. These should be designed to prevent the ingress of contamina- tion and should be easily cleanable (Fig. 13.14), particularly those that are repeatedly touched by food handlers to allow process operation. Fig. 13.12 Examples of unhygienic fasteners. A = Soil trap points, B = Metal to metal, C = Dead spaces. The hygienic design of chilled foods plant 391 The importance of good hygienic design in chilled foods operations can be illustrated with reference to a sliced-meat factory which had slicers whose action was initiated by pressing a control switch identical to that shown in Fig. 13.14. The factory concerned was having problems due to product contamination with Listeria monocytogenes, and was eventually forced to stop production for a few days with a subsequent financial loss in excess of ￡1 million. The problem was finally traced to a source of L. monocytogenes that was being harboured within the body of the slicer switches. At the beginning of production the slicing operative picked up a log of meat, placed it on the slicer and pressed the control switch to start slicing. From this point on, and every time he subsequently repeated this procedure, L. monocytogenes was transferred from his hand to the slicer and, by the middle of the shift, sufficient L. monocytogenes was present on the slicer to be detected in the product. The conclusion to the incident was the purchase of a number of rubber switch covers as shown in Fig. 13.14, for the cost of a few pounds. Fig. 13.13 Examples of hygienic fasteners. 392 Chilled foods 13.5.1 Installation of equipment The potential for well designed and constructed equipment to be operated in a hygienic manner may be easily vitiated by inadequate attention to its location and installation. Timperley (1997), when considering the accessibility of equipment, recommended that it is more effective to consider complete lines instead of individual items of equipment and recommended the following: ? There should be sufficient height to allow adequate access for inspection, cleaning and maintenance of the equipment and for the cleaning of floors. ? All parts of the equipment should be installed at a sufficient distance from walls, ceilings and adjacent equipment to allow easy access for inspection, cleaning and maintenance, especially if lifting is involved. ? Ancillary equipment, control systems and services connected to the process equipment should be located so as to allow access for maintenance and cleaning. ? Supporting framework, wall mountings and legs should be kept to a minimum. They should be constructed from tubular or box section material which should be sealed to prevent ingress of water or soil. Angle or channel section material should not be used. Fig. 13.14 Typical operating switch with inherent crevices (a). Hygienic rubber-capped alternative allowing easy cleaning (b). The hygienic design of chilled foods plant 393 ? Base plates used to support and fix equipment should have smooth, continuous and sloping surfaces to aid drainage. They should be coved at the floor junction. Alternatively, ball feet should be fitted. ? Pipework and valves should be supported independently of other equipment to reduce the chance of strain and damage to equipment, pipework and joints. 13.6 Conclusion As a food preservation method, chilling technology already provides the consumer with a range of products. Both the range and volume of products can be expected to grow considerably in the future together with the need for higher hygiene standards. However, it should be remembered that whilst we may have had over ten years experience in this product sector, chilled foods, like any other forms of preserved foods, have been developed to a high degree of commercial success before all the technical aspects of the system have been fully established or understood. Within the terms of reference of this chapter there is clearly a need for more information on the routes of contamination into high-risk areas and for a greater understanding of the effectiveness of different procedures that are currently used to minimize the ingress of contamination. Similarly, any hygienic design aspects that impinge on the ability of pathogens to survive, grow or be transported around within the high-risk area should be explored. It is also just as important that new or alternative procedures that may be advocated are thoroughly evaluated. Such work would provide the opportunity to bring together the application of the principles of hygienic design with both current micro- biological knowledge related to cleaning and disinfection procedures and industry sectors where microbial or particle control is critical (e.g. pharmaceu- ticals and microelectronics). This could be further advanced by the use of HACCP and mathematical modelling derived from work on predictive microbiology, and a more fundamental knowledge of the microbiological strains capable of growth and survival in chilled environments. 13.7 References ANON, (1983) Hygienic design of food processing equipment. Campden and Chorleywood Food Research Association, Technical Manual No. 7. ANON, (1992a), The Workplace (Health, Safety and Welfare) Regulations, HMSO, ISBN 0-11-886333-9. ANON, (1992b) Workplace Health, Safety and Welfare. Approved Code of Practice and Guidance on Workplace (Health, Safety and Welfare) Regulations 1992, L24 HSE Books ISBN 0-7176-0413-6. ANON, (1995) Food Safety (Temperature Control) Regulations 1995, HMSO, ISBN 0-11-053383-6. 394 Chilled foods ANON, (1997a) Guidelines for good hygienic practices in the manufacture of chilled foods. Chilled Food Association, 6, Catherine Street, London WC2B 5JJ. ANON, (1997b) EN 1672-2. Food processing machinery. Basic requirements. Part 2; Hygiene requirements, ISBN 0 580 27957 X. ANON, (1999), Workroom temperatures in places where food is handled, HSE Food Sheet No. 3 (Revised). ASHFORD M J, (1986) Factory design principles in the food processing industry. In: Preparation, Processing and Freezing in Frozen Food Production, The Institution of Mechanical Engineers, London. BEAUCHNER F R and REINERT D G, (1972) How to select sanitary flooring, Food Engineering, 44 (10) 120–2 and 126. BROWN K, (1996) Guidelines on air quality for the food industry, Campden and Chorleywood Food Research Association, Guideline No. 12. BROWN K L, (2000) Guidance on achieving reasonable working temperatures and conditions during production of chilled foods, Campden and Chorley- wood Food Research Association, Guideline No. 26. BURFOOT D, BROWN K, REAVELL S and XU Y, (2000) Improving food hygiene through localised air flows. Proceedings International Congress on Engineering and Food, April 2000, Puebla, Mexico, Technomic Publishing Co. Inc., Pensylvania, USA (in press). CATELL D, (1988) Specialist floor finsihes: Design and installation, Blackie and Son Ltd., Glasgow and London. EC, (1993) Hygiene of Foodstuffs, Off. J. European Communities, L175, 1–11. EHEDG, Document No. 13. (1995). Hygienic design of equipment for open processing of foods. Campden and Chorleywood Food Research Associa- tion, Chipping Campden, Glos GL55 6LD and as an extended abstracts in Trends in Food Science and Technology, 6:305–10. GUZEWICH J and ROSS P, (1999) Evaluation of risks related to microbiological contamination of ready-to-eat food by food preparation workers and the effectiveness of interventions to minimise those risks, Food and Drug Administration, White Paper, Section One, USA. HOLAH J T, (1998) Hygienic design: International issues, Dairy, Food and Environmental Sanitation, 18 212–20. HOLAH J T, HALL K E, HOLDER J, ROGERS S J, TAYLOR J and BROWN K L, (1995) Airborne microorganism levels in food processing environments, Campden Food and Drink Research Association, R&D report No. 12. IMHOLTE T J, (1984) Engineering for Food Safety and Sanitation, Technical Institute of Food Safety, Crystal, Minnesota. KATSUYARNA A M and STRACHAN J P, (eds) (1980) Principles of Food Processing Sanitation, The Food Processors Institute, Washington DC. METTLER E and CARPENTIER B, (1998) Variations over time of microbial load and physicochemical properties of floor materials after cleaning in food industry premises, Journal of Food Protection, 61 57–65. SHAPTON D A and SHAPTON N F, (eds) (1991) Principles and Practices for the The hygienic design of chilled foods plant 395 Safe Processing of Foods. Butterworth Heinemann. TAYLOR J and HOLAH J, (1996) A comparative evaluation with respect to bacterial cleanability of a range of wall and floor surface materials used in the food industry, Journal of Applied Bacteriology, 81 262–7. TAYLOR J H and HOLAH J T, (2000) Hand hygiene in the food industry: a review. Review No. 18, Campden and Chorleywood Food Research Association. TAYLOR J H, HOLAH J T, WALKER H and KAUR M, (2000) Hand and footwear hygiene: An Investigation to define best practice, Campden and Chorley- wood Food Research Association, R&D Report No. 112. TIMPERLEY A W, (1994) Guidelines for the design and construction of walls, ceilings and services for food production areas, Campden and Chorleywood Food Research Association, Technical Manual No. 44. TIMPERLEY A W, (1997) Hygienic design of liquid handling equipment for the food industry, (second edn) Campden and Chorleywood Food Research Association, Technical Manual No. 17. TIMPERLEY D A, (1993) Guidelines for the design and construction of floors for food production areas, Campden and Chorleywood Food Research Association, Technical Manual No. 40. TIMPERLEY D A and TIMPERLEY A W, (1993) Hygienic design of meat slicing machines, Campden and Chorleywood Food Research Association, Technical Memorandum No. 679, Chipping Campden, UK. TROLLER J A, (1983) Sanitation in Food Processing, Academic Press, New York. 396 Chilled foods