8 Spray Dried Products TOMATO POWDER Tomato powder is much in demand by dehydrated soup manufacturers, and is now produced in many countries where tomatoes are an indigenous outdoor crop. The heavy cropping Italian plum tomato is ideal for drying down to powder, and this is grown in most areas with a ‘Mediterranean- type’ climate. Tomatoes have a very low solids content - not more than 6 percent - and dehydration must be preceded by evaporating the pulped tomatoes down to a paste containing 30 percent solids. Drying to a powder then follows by one or other of the methods described. PROCESS Fresh ripe tomatoes are delivered into a water soaking vat, from which they are conveyed by roller conveyor to a spray washer. After washing, the fruit is discharged to a sorting conveyor where bad tomatoes are removed manually. PULPING At the end of the sorting conveyor, the tomatoes are pulped in a chopping machine, eitherby the ‘hot break‘ or ‘cold break‘ method. The former is more often used with tomatoes for dehydration. The tomatoes are preheated rapidly to about 88°C prior to pulping, and this rapid heating destroys enzymes which prevent decomposition of the pectin. The latter’s retention helps to give body to the paste. The cold break method, by which thc fruit is pulped at room temperature, produces a paste which is easier to spray but, when dried, the 192 powder will not reconstitute so well, the solids tending to settle out rather than remain in homogeneous suspension. The cold break method has some merit in the manufacture of tomato juice, in which it often produces a better colour and flavour but it invariably has a tendency to cause separating out. STRAINING From the pulper the material passes to a holding tank, thence to a series of strainers with perforated plates, reducing consecutively from 1 mm holes to 0.7mm and finally to 0.4mm. This process removes the skin and seeds, amounting to 5 percent of the weight of the fruit. Strained pulp is then transferred to storage tanks. EVAPORATING The juice is concentrated under vacuum from 5 to 30 percent solids, as a preliminary stage to drying. A double-effect evaporator is normally used, with a finishing pan in the final stage. From here, the paste is transferred to a feed tank where it is constantly mechanically stirred. SPRAY DRYING OF TOMATO POWDER The flow-sheet drawing Fig. 8.1 showsanoperation whereby the production of tomato powder is continuous and concurrent with the evaporation of the fresh pulp. In practice, however, some producers of tomato powder make their product out of season, and in the case of a plant in Portugal, which the author has visited, the company bought in most of their concentrate from a nearby tomato paste factory where there was a surplus, over and above what was contracted for export, as concentrate in 5kg cans. The cans were delivered to the drying plant in standard 5kg packaging, opened by a piston-type automatic can opener, which ejected the paste into the storage vat serving the dryer, at the same time crushing the empty cans and baling them for disposal. In this case the process commenced at Figure 19 on the Flow Sheet - Feed Tank for the Spray Dryer. In this particular instance the concentrate was made by the hot break system with concentration to 30-32 percent solids. Cold break pastes, concentrated to 36-38 percent concentration before drying, are sometimes used. 193 Fig.8.1: Process flowsheet for producing tomato powder from fresh tomatoes by spray dying IStF.0. SllNl MlEE Key to Figure 8.1 1. Soaking vat 2. Roller conveyor stirrers 30. Spray-drying chamber with 3. Spray washing vat 18. Transfer pumps double wall 4. Air compressor 19. Feed tank for spray dryer 31. Exhausted drying air duct 5. Sorting table 20. Water tank 32. Cooling air fan for item (3 1) 6. Chopper 21.Three way valve 33. Cyclone with pneumatic 7. Preheater 22. Feed pump to atomiser transport conveying at base 8. Intermediate holding tank 10. Coarse mesh strainers 11. Medium mesh strainers 12. Fine mesh strainers 13. Holding tanks 26.Supply from air filter 39. Powder sieve 14. Doublehriple effect evaporator 27. Supply air fan 15. Finishing pan 16. Transfer pump gas air heaters arc altemativcs) atmosphere 17. Intermediate storage tanks with 29. Drying air disperser 23. Atoiniser (rotating vaned disc 34.Exhaust drying air fan 35. Exhaust duct and air hood 24. Supply air inlet (cooling spray 36. Band conveyor (air conditioned) 37. Packing room (air conditioned) 25. Supply air from atmosphere 38. Air conditioning unit 40. Powder packing box on scale 41. Chamber for packing in an inert 9. Transfer pump tY Pe) drying chamber walls) 28. Steam-air heater (indircct oil- By couvtesy of Niro Atoiniser Above: Batch evaporator plant Niro Dryer There were two of these dryers in parallel in this particular plant, and the Niro dryer is specially designed to cope with the properties of tomato powder, with a drying chamber of non standard construction as compared with other types of spray dryer. The conventional chamber design would create problems on account of the thermoplastic and hygroscopic properties of the powder, and continuous drying would be difficult. The co-current drying chamber (30) has a jacketed wall for air cooling and a conical base. Ambientair isdrawn through the jacket prior toentering thechamber via the air heater (28). Cooling air intake is controlled to enable close maintenance of a wall temperature which, in the range of 38'- 50°C, allows continuous operation. Paste is pumped to a rotating vaned-disc atomiser (23) located within the air disperser (29). The vaned disc has multi-vanes to achieve complete atomisation of the heavy paste feed. Paste is sprayed into the drying air entering the chamber at a temperature of 138'- 150°C. The drying air to the 195 heater (28) is supplied from the cooling air wall jacket supplemented by atmospheric air intake. The location of the atomiser within the roof air disperser creates optimum spray/air contact conditions. Moisture evaporation is rapid but controlled. Product settles out of the air-flow on the chamber wall, building up to loose layers (15 - 25mm thickness) before breaking away and falling as nodules to the base of the chamber. The build-up is important for completion of evaporation. For the removal of the remaining moisture from a tomato particle, much resistance to mass transfer is apparent. The necessary long second period of drying is accomplished by the residence timeon the cooled wall. Increased drying temperatures cannot be used as heat degradation wouldresult.15-20percentof the throughputdoesnot settleon thewalland passes out of the chamber with the exhausted drying air. The entrained product is recovered in a cyclone, and conveyed from the cyclone base in dehumidified air. The bulk of the production falls from the chamber base into an enclosed band conveyor (36). Cool dehumidified air flows counter-currently slowly over the surface, and the product nodules are cooled on the conveyor. Ata temperatureof24"-3OoC, the nodules become brittle,and readily shatter into powder as they fall from the conveyor on to a sieve (39). This conveyor exit and sieve are installed within an air conditioned packing room kept at a low humidity. The plant under review dehumidified this area to 30 percent RH, with the temperature at 15°C. Insome plants this dehumidified area is treated with sodium fluorate, which is introduced into the air flow to provide a sterile atmosphere. Finalmoistureof the powder is3 to3.5 percent, and to maintain this low level in a hygroscopic material, it is preferably packed in nitrogen-flushed sealed polyethylene-lined drums or tins. Whatever container is used it must be air and moistureproof. Atmospheric packing in very dry air conditions was practised at the factory visited but this is recommended only for limited storage periods. Anticaking dessicants can also be used, in the form of silica gel envelopes placed in each pack. Overall Ratio: range from 20:l to 22:l (Raw material to powder) Whilst the drying plant was equipped to process from 5kg cans of concentrate, a more economical method of packing of the concentrate by the supplier would be in asceptic 225 litre barrels. These are filled at the concentrate plant by flash sterilising the paste at 95"C, cooling to 40°C and filling intopresterilised barrels under reduced pressure. A vacuum is drawn through a 20mm aperture in the top, and filling is through a second 50mm 196 aperture. In the event, the latter method was advised and implemented the following season. Above: Spray dryer for production of tomato powder INSTANT COFFEE CLEANING AND BLENDING The first step in the processing line is a thorough cleaning of the green coffee beans, to removedefectivebeans and extraneous matter. Blending is usually carried out to achieve optimum flavour development in the roasting stage. RO&TIJXGANDGRINDING Roasting enhances the flavour and aroma and may be carried out batch-wise or continuously. The latter continuous method is more cost effective. Grinding to a particle size most suitable for the extraction process follows. EXTRACTION This is eithercontinuousorbatch. Thecontinuous method employsa tiltable jacketed pressure vessel containing two helicoidal conveyors. Hot water enters the top end and the extract flows through the trough by gravity. The dwell time is from 30 to 40 minutes. In two stage extraction, atmospheric pressure is used in the first stage and pressure in the second. Batch extraction is carried out in a counter-current column battery unit featuring split extraction under closely controlled conditions, and yields of over 48 percent can be achieved. The first stage produces a prime quality extract, which is held separately pending final pretreatment and drying. The second stage produces a high overall extract yield but with low solids and this has to be subsequently concentrated. CONCENTRATION Two methods are used, eithera two stage falling film evaporator with aroma recovery section, or a rotary thin film evaporator designed uniquely by Niro for heat sensitive products. Both types of evaporator operate undcr vacuum, thereby maintaining low extract temperatures. SPRAY DRYING The concentrated extract is pumped to the pressure nozzle in the drying chamberwhereit isatomizedand contacted with hot air. Drying temperatures are low in order to preserve aroma and flavour in the dry product. An in-line spargesystem operating with inert gas in the feed system allows adjustment of powder bulk density and colour. The enlarged conical section of the drying chamber separates the dried coffee from the drying air so effectively that virtually all the powder leaves the base of the chamber, where it is cooled, screened and passed to storage, packing or agglomeration. 198 Efficient cyclones clean the air, preventing the emission of coffee fines to the atmosphere. Heat recovery systems can be installed to preheat the inlet drying air, whereby energy savings of 15 to 20 percent can be made. As related in Chapter 4 (Dryers) energy costs can be cut by recovering the spent grounds from the extractor plant, to produce a cheap fuel for steam generation, if the boiler plant is normally fed by fossil fuels. AGGLOMERATION This is carried out by wetting the instant dried powder with either water or coffee extract and after-drying in a fluidised bed dryer. The degree of agglomeration is controlled to give the product the appearance of regular ground coffee. Agglomeration improves the solubility factor, and simulates fairly closely the appearance of freeze-dried coffee. The Figure 8/2 shows a production line without agglomeration. A medium sized plant would perform as under: Green coffee (10% moisture) input 595kg per hour Roasted coffee (6% moisture) input 520kg per hour Extract solids content (split extraction) 10 / 25% Green Coffee yield: 2.38:l ratio = 42% Concentrate solid: 36% Spray Dried powder rate: @ 3% moisture. 250kg per hour Annual production: based on 270 days/6500 hours production time = 1625 tonnes. An agglomerator f. 6 x a vi E 8 tj E 2 3 3 .L, E iE I: s 6 .E! Y 4 4 12 I: z * a e E wh B 2 "! cg .9 U .- I In 5 200 SKIM MILK POWDER Skim milk powder accounts for about 80 per cent of the global production of milk powders; dried whole milk, butter milk and whey comprising the balance. 2 In 1987 it was reported that some 100,000 tonnes were in EEC intervention storage, being surplus to commercial consumption requirements. The latter fluctuate widely from year to year. Milk quotas throughout Western Europe have been adjusted to correct this surplus situation but the technology in spray drying has recently been so much improved that new outlets for dried skim milk are being progressively created. Whey powder also has found many new uses with manufacturers - in ice cream mixes for flavour enhancing, in bakery products as a shortening agent, in soup and sauce mixes, and in dessert topping products. The new technology in spray drying has also given more choice to the buyer in that, for specific end uses, he can now specify low heat, medium heat, or high heat powder. This is made possible by the introduction of multi-stage dryers, as indicated in Chapter 4 (Anhydro Spray Drying Systems). The process herein described is based on the author’s contact with skim milk production in 1981, and whilst the spray dryers in this particular plant were not of the design described in Chapter 4 they were efficient and met the requirements of the processors, who were a company manufacturing a milk- based value-added product, and the Dairy Marketing Board, who absorbed any tonnage surplus to commercial sales. PRODUCT HANDLING It is customary for most drying plants to be located alongside the dairy in which the whole milk is processed, either for straight consumption, or con- version to cream, butter and cheese. In this particular case the dairy is located some 500 metres from the drying plant, both companies being in separate ownership. The drying plant has a long term contract with the dairy to supply 70 million litres of skim milk (or 92 percent of the creamery’s capacity) per annum. This is fed into the drying plant by a pipe line, and subsequently into buffer storage tanks, refrigerated to 5°C. The incoming skimmed milk has a minimum 8.8 percent solids and its specific gravity is 1.035. The supply is subject to seasonal peaks and troughs, which precludes continuous operation throughout the year at 100 percent capacity. In some circumstances, this could be corrected by an intake of skim milk in tankers from other creameries but the location is isolated and not contiguous to other creameries to make this a viable operation. Shifts are therefore reduced from 3 to 2 in the late winter months, and the late autumn. In the normal way, had the company been dependant only on the sale of straight skim milk powder, this partial restriction of supplies would have been less than economic but the additional production of a value-added item balances out any loss which might be occasioned by an interruption of the spray drying process. This production unit in Northern Ireland was monitored by the author for the purpose of a valuation and viability, commercially. The process is set out as follows: The Skim Milk was evaporated with a 'falling film' evaporator to a concentration of 45-46 per cent total solids. The falling film concept made it possible to operate with low temperature differentials and to achieve high thermal efficiency. Manual supervision of the equipment was minimal, and the start-up, shut-down and C.I.P. could be automatically performed. The evaporator serving the first of two spray dryers was a 4-effect unit, with a three stage instantizer, following the second spray dryer. Initial pasteurization time before evaporation was at 71°C for 15 seconds. This No 1 plant handled 19,350kg of skim milk (at 8 per cent total solids) per hour yielding 1,820kg of powder at 4 per cent moisture per hour The maximum inlet temperature of the drying air was 93°C with an outlet at 82°C. At these temperatures the evaporation was approximately 1,865kg per hour and the yield of powder at 4 per cent was 1,820kg per hour - a conversion ratio of 10.63:l. The steam consumption was 3,950kg per hour for the dryer and for the evaporator 3,045kg per hour. Installed power was 240KVa. The No 2 plant was smaller with a two stage instantizer. The efficiency of the dryer was similar to the No 1 plant with an input of 7,727kg per hour and a yield of 650kg per hour, although the evaporator was slightly less efficient in that it consumed rather more steam per kg of water evaporated. Steam consumption was 1,600kg per hour for the dryer and 1,900kg per hour for the evaporator. Installed power was 95KVa. Packaging was in polyethylene-lined multi-ply paper sacks. Bulk stor- age silos had a capacity of 70 tonnes, and the warehouse had a capacity for 2,000 tonnes of product. The storage of raw milk as previously indicated only provided for 28 hours reserve, and comprised 4 stainless tanks - 2 of 114,000 litres capacity and 2 of 91,000 litres, and this feed stock was maintained at 5°C. HYGIENE Clean down procedures were carried out daily on the evaporating plant; 4 hours wash-down after 20 hours running. The spray dryers were cleaned down as necessary at least every 4 weeks. QUALITY CONTROL Tests on raw milk include: acidity, total solids, water adulteration, temperature and full bacteriological tests. In-process tests include total solids in the concentrate. 204 STAFFING Total personnel, including management, is 67 at peak production times, of whom 28 are permanent staff. The balance are, in this instance, seasonal workers. Whilst the foregoing relates to an established spray dried milk plant in operation for some 13 years, a processor intending to engage currently in such a project, should obviously evaluate market conditions, and furthermore study the evolution of spray drying plant as recently outlined by APV Anhydro and set out in detail in Chapter IV. The author has always endeavoured to set down in the text the experience gained from practical contacts with operational plants but the reader should also be aware that technology advances almost day by day, and practices of even a year ago may be approaching obsolescence today. A mere guide to processes and disciplines is all, therefore, that can be achieved in a text book of this nature. POTENTIAL USES FOR SKIM MILK POWDER Agglomerated Skim Milk has been boosted in recent years by the public’s trend to reduce their intake of fatty dairy products -butter, cream, cheese and full cream milk - on health grounds. A high fat diet has been regarded, along with other factors, as contributing to obesity and heart disease. High fat and sucrose intake by children is thought by some nutrition experts to affect behaviour patterns and mental concentration capacity. Specimen diets, studied by medical specialists in nutritional problems, and containing high fat and sucrose constituents have also indicated a deficiency of certain vitamins and chemical trace elements which are necessary for a ‘balanced’ diet. The validity of these claims has yet to be proved by a wider field of investigation than has hitherto been undertaken but the low fat diet theory appears to be well founded and accepted by many people. This has given an impetus to the sale of liquid low fat milk and aggressive advertising has created a substantial market for dried agglomerated skim milk. Agglomeration ensures the immediate dispersal of the milk solids in water, and the product is instantly soluble by the addition of cold water. The bakery and ice cream industries are substantial users of skim milk powder, in addition to the other creamery by-products, whey and butter milk, which in dried form have many uses. In the light of the still-mounting stocks of milk powder in intervention storage, the author has been involved in seeking interest in projects for reconverting milk powder into liquid milk, by rehydration and the addition of butter fat, then sterilising it and marketing the product in regions of high population in the developing countries, where little or no fresh milk is available. One project was in Cairo, which has a population of some 10,000,000, 205 increasing at times to 12,000,000, by an ingress of some two million 'floating' population. In 1982 there was only one small processing plant involved in the rehydration of milk powder in the manner suggested, and the food stores have insufficient fresh milk to sell owing to the few dairy herds in existence. The small reprocessing plant, packing reconstituted milk into 1 litre UHT retail packages, which require no refrigeration, seems to fill a definite need. An expanded scheme for Cairo and other major centres of population was the subject of a feasibility study which envisaged a plant producing 8000 litres of UHT milk per hour from skim milk powder with 6 percent of the productive capacity of the plant diverted to the manufacture of ice cream and yogurt. The project purported to show that the reconstituted milk, brought up to the required butter fat content, could be produced at a price more than competitive with fresh milk locally produced or imported. UHT milk would be available to millions of people at a price they could afford, in a market which is somewhat short of reasonably priced dairy products. This scheme envisaged the production of the following products: (1) UHT 1 litre packs of milk manufactured from skim milk plus anhydrous (2) Evaporated Milk, milk fat and water, this product to be either plain or flavoured. Sweetened Condensed Milk, Recombined butter and butter-type spreads, Baby Foods, Recombined Cheeses (3) Yogurt - either zero-fat yogurt, or maximum 2 percent fat hard, 'scoopable' ice cream yogurt. (4) Ice Cream and Ice Cream Mixes MARKETS Investigations showed that supermarkets, stores and hotels would accept these products, not only in Cairo, but in Alexandria, Ismalia and other major centres of population. EXPORTS Exports might eventually be feasible to other Middle East countries. The process and plant for 'recombined' milk, as it is technically described, has been developed by a multi-national dairy engineering plant company, and is described hereunder, and is also referred to in Modern Dairy Products (1975) published in the USA. Four stages are involved: (1) Mixing of raw materials: (2) Uperisation: (3) Aseptic Tank Storage: (4) Packaging. 206 MIXING To produce a recombined milk with 3 percent butter-fat content, the raw material required for 16 million litres (assumed production per annum) would be 1616 tonnes Skim Milk Powder 480 tonnes Butter Oil. The raw material mix, therefore, will be 77.1 percent milk powder and 22.9 percent butter-oil. Mixing is effected in a Liquiverter - a stainless steel hopper, incorporating a rotary impeller in the base, which feeds the material in the above proportions into two reconstitution tanks with paddle agitation. Circulating pumps and a steam heated circulation heater provide the energy and heat for this operation. Water flows from one of the reconstitution tanks to meet the dry material fed into the Liquiverter, where lumps are broken down by the impeller before the flow is reversed and the mixture pumped back into the tank. During the circulation the heater raises the temperature to 55". The mixture is then transferred to the Uperisation unit, whilst the second reconstitution tank is brought into use for the following batch mix. UPERISATION This is a method of continuous sterilisation by injection of clean live steam into the product. Vapour equal to the amount of steam injected is removed during cooling - thus preventing dilution of the milk or over-concentration. Rapid heating and cooling, with a short holding time ensures that flavour and appearance are not affected. After preheating to 77-80°C the milk is pressurised by a booster pump before passing into the Uperiser, where steam is injected, raising the temperature to 150°C. After a short holding time, the product is 'flashed' off into the expansion vessel, and cooled to 80°C. In this vessel the same amount of vapour is removed as was injected by steam. The milk is then homogenised, cooled in a plate cooler and transferred to the aseptic tank system. ASEPTIC TANKS These provide a buffer store of milk between the Uperiser and the packaging Machines. In operation, the tanks and associated pipework are first flushed with sterilising fluid, and the sterile condition is maintained by sterile air. Constant air pressure ensures a steady flow from the tankage to the packaging plant. 207 -t s _._~ - 5- I 13 - .~ Figure 8.4 - Key to Figure 8.3 1. The roll of packaging material is located in a cassette at the back of the machine. 2. A photocell, which gives a signal when it is time to insert a new roll of packaging material. 3. Rollers which soften up the creases in the packaging material, thus facilitating final shaping of the cartons. 4. Stamping device, which stamps the packaging material with the date or other marking. 5. Bending roller. 6. When the splice between two rolls of packaging material passes this point, this is registered by the machine. The carton which is subsequently sealed by the spliced packaging material and the two succeeding cartons are discharged through the drop chute 20. Strip applicator, in which one edge of the packaging material is provided with a plastics strip. This is subsequently sealed to the other edge of the packaging material. In the sterilizing bath, the inside of the packaging material is wetted with hydrogen peroxide. The wetting process is monitored by a built-in control function. 9. Rollers which mangle away any surplus hydrogen peroxide. 10. Cover for collection of air rising from the paper tube. This hot air is returned to the sterile air compressor and, in conjunction with this, any residual hydrogen peroxide in the air is removed by washing with water which is collected in a special separator. 7. 8. 11. Upper bending roller. 12. The product to be packed is introduced through the stainless steel filling tube, which is jacketed by a second tube through which sterile hot air can be blown into the paper tube. The current of air is deflected upwards upon reaching the lower edge of the tube heater. 13. As an initial stage in the sealing of the longitudinal seam, one edge of the packaging material passes through an element which is heated by hot sterile air. 14. The longitudinal seam is sealed in this forming ring where both edges of the packaging material are pressed together. 15. The tube heater consists of a coil-shaped electric element that heats the inside of the packaging material with radiant heat. This radiant heat sterilizes the packaging material and at the same time a sterile atmosphere is created above the liquid level. 16. Liquid level in the paper tube. 17. The liquid level in the paper tube is regulated mechanically by a float SO 209 that it is always higher than the mouth of the filling tube. By this means, frothing is avoided. 18. Filling-tube mouth. 19. The cartons are finally sealed below the liquid level and are thus completely filled. Sealing is carried out by a system of jaws, which also separate the cartons. 20. Upon commencement of a production run, and when the packaging material contains a splice, the cartons are discharged here. 21. The finished cartons are discharged from the machine, either to the right or to the left, and carried by a conveyor to the place where they will be packed in transport packaging. Fig 8.5 Sterile air system for 1 litre packs 210 Key to Figure 8.5 1. The compressor which creates the necessary pressure in the sterile-air system is of the water-ring type, implying that in order to function it requires a continuous water supply at a rate of approximately 8 litres per minute. The water serves a twofold purpose: not only does it afford a seal between the rotating impeller and the pump housing but it also washes away any residual hydrogen peroxide contained in the air sucked in from the upper part of the machine at 17. 2. Water inlet to compressor. 3. Separator for removal of water from the air. 4. While the machine filling system is being sterilized prior to commencement of production this valve is open and the water is discharged to the drain. During production, the water is used as coolant in the cooler 17, after which it is discharged into the drain. Heater in which the air is heated to approximately 350°C. Some of the heated air is conducted to the strip applicator and longitudinal sealing element of the machine. Cooler, in which the air temperature is lowered to approximately 80°C. This valve is open while 1 litre cartons are being produced and conducts the sterile air into the space above the liquid level in the sealed paper tube. On machines for making smaller carton sizes this valve is closed during production. The filling system is sterilized with hot air before commencement of production, and during the process this valve is open. 5. 6. 7. 8. 9. 10. Filling tube for the product to be packed. 11. The sterilized air is supplied through this tube which completely encases the filling tube. 12. The electrically heated, coil-shaped tube heater element emits radiant heat which sterilizes the inside of the packaging material. 13. At this point, the current of sterilized air in the paper tube is deflected upwards. The vaporized sterilizing liquid is removed, and at the same time a sterile atmosphere is created in the sealed paper tube. By this means, re-infection from the air in the premises is prevented. 14. Liquid level in the sealed paper tube. 15. Float which regulates the liquid supply through the filling tube. This float 16. Throttle-type valve. 17. Cover which collects the air rising from the sealed paper tube. This air is returned to the compressor 1, where it is mixed with water which washes away any residual hydrogen peroxide. The water is then collected in the separator 3. communicates with valve 16. 21 I