I1 Selection, Pac kagi ng and Storage SIEVES The size grading of dehydrates is an important function, both in the interests of quality and presentation, and also for the purpose of obtaining the optimum return on products undersize, or less than the standard cut. With almost all cut vegetables and fruits, there will be off-cuts from the dicers or cutters, which can be effectively separated from the primary product by the use of effective sieving machines. The recommended type of sieve for all dehydrates, whether whole product, diced, sliced or comminuted, is a high centrifugal force vibratory screen with adjustable amplitude and pitch. The Russell Finex 22 as illustrated in Chapter 5 is ideal for screening potato granules in the final stage of sifting the potato mash powder through a 250 micron or even finer mesh, whilst the Finex 48 Vibro Separator with two decks is highly recommended for the initial stage of screening the blend from the primary dryer, from which point one fraction returns to the mixing plant and the other to the secondary dryer and then to the final screening. The Finex 48 is also very effective as a screening machine for all vegetables and fruits after bin drying and aspiration (where applicable) and before the final inspection and packing. Again, this machine has adjustable amplitude and pitch for any desired flow pattern, which is absolutely necessary to obtain perfect size separation. Deblinding devices can be fitted 225 to both types of screen for products which are prone to ’blind’ the mesh during extended usage. The illustrated self-loading sieve is also suited to handling granules and powders, which are fed into the lower bin and then drawn up to the dust-tight gallery above the mesh of the self-loading sieve by vacuum. The air is separated from the material via an integral filter mounted in the lid of the sieve and taken away either by a venturi or electric vacuum pump. A timer control switches off the vacuum and sieved material drops into a suitable container sited below which, in the case of potato granules, could be end packaging sacks and liners. This type of arrangement may suit some lay-outs but is invariably regarded as more suitable for granules or powder than cut products. A useful range of sieves for dehydrated vegetables and fruits is as follows: Round-hole screens: From 4mm to 9mm in increments of 0.4mm - stainless steel. Slotted screens: 19mm by 2.5mm and 25mm by 3mm - stainless steel. Woven wire screens: 1.5mm, 1.2mm, lmm, 0.85mm - stainless steel. The above would cover the screening of most types of fruit and vegetables. For Potato Granules and Powders the sieves range between 350 microns to 150 microns. A 250 micron screen is commonly used for the pack-off granules in the final sieving. Powder screens may be stainless steel or occasionally nylon. The processor must select the size of screen most suitable for the product being graded, bearing in mind what outlets there are for the ’through’ material with any particular size of aperture. Some off-cuts from 9.5mm dice, for example, are useful for soup formulations, where the particle shape may not be too critical. For a quality soup, however, the vegetable is usually cut to the appropriate size, initially in the raw state. When screening 9.5mm carrot dice (in the dry state), with a 4.8mm sieve on the top of the screen, about 10 percent will pass through as off-cuts or ’Small cut’, and a rather smaller percentage when sieving potato. With a 6.4mm sieve fitted, up to 20 percent will pass through. The decision on which to use, can only be made in the light of circumstances, taking into account the buyers’ specification for the appearance and size of the main product, and what outlet there may be for the smaller particle fraction. In addition to these two fractions, using a twin deck screen, a 1.2mm screen can be used at the lower level to take out fines which can be milled for vegetable powder in a Turbo Mill. 226 SELECTION Manual and visual selection of some dehydrated products is still necessary, as the particle size may not lend itself to electronic colour sorting. The latter method can be adopted for free-flowing material, such as dice, peas and some flaked vegetables, but is unsuitable for strips, rings and leaf products. Manual selection of dehydrates is carried out on PVC-coated inspection belts 7m long and 60cm wide for a medium throughput. Ideally, these belts should be fitted with a feed hopper incorporating a vibrating tray or chute, giving a controlled and metered feed of material across the belt. Bucket and belt elevators, and auger feeds, should be avoided in conveying diced material at any point of the process, as these cause severe abrasion and loss of product, and they are difficult to clean. A well-designed elevator, with moulded rubber flights, or a spiral vibratory elevator are the only satisfactory means of elevating and conveying dry materials. The selection belts should accommodate a team of women on either side and there should be good natural light in day-time, as the inspection is tedious and liable to cause eyestrain in poor light. Whilst white is an hygienic colour for belts, it may be found beneficial to use other colours which will highlight the blemish that has to be removed. There is always a risk of metal abrasion in the plant at some point or another, and it is essential to have a series of powerful permanent magnets fitted on the selection belts. One of these should bridge the belt, across its width, just high enough to allow the material to pass underneath. At the end of the belt, where the material discharges, it is a wise precaution to have a second pair of magnets set at about 45" to each other, over and under which the product cascades into the collecting hopper. These magnets will, of course, only abstract ferrous metal, and most processors install a more sophisticated electronic detector for all types of non ferrous foreign matter which may pass over the belt. These detectors are designed to stop the belt when any extraneous matter is detected, and it is then manually removed. The speed of the selection belts should be from 4 to 5m per minute, according to the capability and availability of the staff and the means of selecting efficiently. The recommended loading rate for onion slices, for example, is 250g per metre of belt length. ELECTRONIC COLOUR SORTING This method has made tremendous strides in the last five years, and Sortex Ltd of London are specialists in this field, having made an extensive study of the dehydrator's requirements. Their machines are capable of efficient throughputs of vegetable dice, flakes, peas and particles smaller than dice, although in the latter case the 227 throughput is obviously restricted, as each particle has to be scanned individually. Some types of optical colour sorters operate by feeding material through an optical box fitted with sixteen photo-electric cells, for each of 10 chutes, which scan the surface colour of the product against automatically adjusted backgrounds. Pieces which are ‘in-balance’ as to colour, pass through an ’accepted’ delivery chute at the bottom of the machine, and those which are ‘foreign’ to the background are blown out of trajectory, by a fine jet of electronically signalled compressed air, through a ‘reject’ spout at the back of the machine. Modern machines may operate from a common feed, and have a throughput capability of 1200kg per hr with some types of vegetable dice cut to 3/8in. by 3/8in. by 3/8in (10mm cubes). . These machines are progressively replacing manual inspection of dehydrated vegetables as they are infinitely cheaper to operate. Some final visual inspection is always advisable, however, after the product leaves the colour sorter but this is mainly a ’policing’ operation, and only makes minimal demands on staff. The use of electronic sorters, however, demand the employment of highly skilled personnel to service them. Air Separation Some products lend themselves to quality grading and selection by aspiration, and very efficient machines are now available for this purpose. It sometimes happens that the fraction of material to be abstracted from a product has a different specific gravity from the acceptable fraction. A finely balanced air separator will deal with this abstraction very adequately, and will save hours of manual selection. Two examples of this are the coarse core pieces present in cabbage, and the green fraction of leeks. Both of these fractions can be eliminated by aspiration and air separation. PACKAGING Both materials and units of packaging must satisfy a specific set of requirements: (1) They must be compatible, costwise, with the value of the product they are designed to carry; (2) They must give protection against the ingress of moisture, light, air and infestation by vermin and insects; (3) They must be sufficiently strong and stable to protect the product from damage by abrasion, and a considerable degree of handling in store and in transit; (4) Materials must be approved for contact with a food product; 22% (5) Size and shape must be acceptable from a distribution and storage point of view. BULK PACKAGING Peas, vegetable dice and small cuts, granules and flakes are usually packed in multi-ply paper sacks with a polyethylene liner inside. This packaging is acceptable where the abrasion factor is low but it is not so suitable for such products as onions, green beans and cabbage. A suitable specification for a 5-ply paper sack for dehydrated vegetables is: 1 outer ply 361b wet strength kraft; 1 inner ply 521b Union kraft (bitumen impregnated); 3 inner plies 361b natural kraft. Above specification is based on UK standards. Above: Vibratory packing table made by Valley Products Ltd for the consolidation of bulk materials; it is suitable for packing dehydrated products in tins. 229 The optimum packing weight is usually about 25kg for this type of sack, which will measure approximately 114cm by 68cm by 9cm (gusset) for diced root vegetables. The polyethylene liner for this sack is normally of 300 gauge, and preferably pigmented to keep out light. Buyers should avoid the acceptance of liners made from regenerated material, as pigmented polyethylene is often made from reprocessed scrap and should be graded accordingly. The liner should be tightly secured at the neck by a non-metallic fastener after filling with product, and then the sack must be stitched along its mouth. The more delicate materials, such as onion, green beans and cabbage, which are all subject to abrasion and handling damage, should be packed in polyethylene-lined fibreboard drums or cartons, the net weights varying between 8 and 10kg. Above: A Valley Products’ horizontal vibratory feeder equipped with a small bulk feed hopper 230 Should larger packs be required, for shipping economy, then the above weights may be exceeded by using fibreboard drums, with metal reinforced ends and a polyethylene liner inside. These drums have the merit of rigidity, and give the product good protection but they are cumbersome to stack in warehouse and in transit. Reference has been made earlier to packing in tinplate containers but the current cost of tinplate almost precludes this, except for high value material, for example, meats, poultry and special vegetable packs for export to the tropics, or for storage in exceptional conditions. The standard dehydrator’s tin is a nominal 18 litre capacity container, 23cm by 23cm by 33cm high, with a 15cm aperture for filling, and a lever lid to fit this aperture. These tins, which are normally nitrogen-flushed after filling, give excellent protection on all counts, and they ensure a shelf life of 12 months or more for the product. Against these factors must be balanced the cost of the container, the fairly high labour cost of filling, gassing and soldering, and the fact that it is not easy for the user to empty the tin of its contents completely. The 15cm aperture never appears large enough to eject the last few ounces of product lodging in the square corners of the tin. Another objection by users is that the soldered tagger plate is difficult to remove. An alternative tinplate container is the nominal 5kg open top can, which can be easily filled, hermetically sealed on a double seamer and nitrogen- flushed through a brogue hole in the end. This container is, however, too small for most vegetables, other than potato granules, but it is ideal for meat packs. Packaging for retail and small catering packs may be selected from a wide range of materials, including polypropylene film, cellulose and polyethylene film, and laminates of many types. A dehydrator must take into account the barrier properties he requires, before deciding on a film or laminate, and he must also establish what shelf life a particular form of packaging will provide. The shelf life of retail and catering packs of vegetables is normally guaranteed for nine months, and this requirement must be considered when selecting packaging material. The only satisfactory way to establish suitability is to undertake accelerated storage tests, by incubating products in test packaging and logging the results at prescribed intervals. It is possible to nitrogen-flush small packs, with suitable equipment, where it is found necessary, to inhibit oxidisation. Low moisture content is, in the ultimate, the major requirement for satisfactory storage of all dehydrated foods. Low temperature storage conditions are also important. Ideally, warehouse temperatures should not exceed 10°C and, in hot climates, some cooling equipment is necessary in stores. 23 I Dry conditions and low relative humidity are essential, and all warehouses should be serviced to prevent rodent and insect infestation. Failure to do this can cause extremely heavy financial losses. Pybuthrin is an effective aerial spray to control most flying insects, and this should be used weekly throughout the whole of the factory and warehouses. It is non-toxic but the application should be given whilst the plant is closed down at weekends, as it can have unpleasant effects on personnel whilst the spray is in suspension. The operator should wear a suitable mask whilst using the spraying equipment. Rodent control should always be carried out by specialist contractors, as this can rarely be done satisfactorily by factory personnel. 232