Spray Dried Products T。 MATO 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, either by the ' hot break'or'cold break'method The former is more often used with tomatoes for dehydration. The tomatoes are preheated rapidly to about 88C prior to pulping, and this rapid heating destroys hich prevent decomposition of the pectin. The latters retention helps to give body to the paste The cold break method, by which the fruit is pulped at room temperature, produces a paste which is easier to spray but, when dried, the
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 ‘Mediterraneantype’ 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 1mm 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 ransferred 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, h 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 shows an operation 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 thedrying 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 ca 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 stem with concentration to 30-32 percent solids. Cold break pastes, concentrated to 36-38 percent concentration before drying, are sometimes
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
Fig8.1: Process flowsheet for producin 君「「 TDNATO d Key to Figure 8.1 17. Intermediate storage tanks with 29. Drying air disperser 18 Transfer pumps 19. Feed tank for spray dryer 31. Exhausted drying air duct 2. Cooling air fan for item (31) 8. Termediate holding tank 23 Atomiser(rotating vaned dise 34. Exhaust drying ainf an base air inlet(cooling spray 25 Supply air from atmosphere 38 atoning unit Supply from air filter le effect evaporator 27. Supply 15. Finishing pan 41 Chamber for packing in an inert gas air heaters are alteratives By courtesy of Niro Atomiser
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 oilBy couvtesy of Niro Atoiniser
豐里 Above: Batch evaporator plant Niro Drver 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-curren drying chamber(30) has a jacketed wall for air cooling and a conical base. Ambientairis drawn through the jacket prior tentering 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"-50C, 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
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 ofthe chamber. The build-up is important forcompletion 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 time on the cooled would result. 15-20 percent of the throughput does not settle on the walland 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 Atatemperatureof24-30C, 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 15C nsome plants this dehumidified area is treated with sodium fluorate, which is introduced into the air flow to provide a sterile atmosphere Final moisture of the powder is 3 to 3. 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 ised at the factory visited but this is recommended only fo storage periods. Anticaking dessicants can also be used, in the form of silica gel envelopes placed in each pack Overall Ratio: range from 20: 1 to 22: 1(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 asceptic 225 litre barrels. These are filled at the concentrate plant by flash sterilising the paste at 95C, cooling to 40C and filling into presterilised barrels underreduced pressure. A vacuum is drawn through a 20mm aperture in the top, and filling is through a second 50mm
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
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 remove defective beans and extraneous matter. Blending is usually carried out to achieve optimum flavour development in the roasting stage ROASTINGAND GRINDING Roasting enhances the flavour and aroma and may be carried out batch-wise orcontinuously. The lattercontinuous method is more cost effective. Grinding to a particle size most suitable for the extraction process follows EXTRACTION This is either continuous or batch. The continuous method employs a 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 ressure is used in the first stage and pressure 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 concentrate CONCENTRATION recovery section, or arotary thins stage falling fiImevaporatorwitharoma evaporator designed uniquely by niro for heat sensitive products Both types of evaporator operate under vacuum, thereby maintaining low extract temperatures SPRAY DRYING The concentrated extract is pumped to the pressure nozzle in the dryin chamber where it is atomized and contacted with hot air Drying temperatures are low in order to preserve aroma and flavour in the dry product. An in-lir sparge system 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
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 coffeefines 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 forsteam 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 1 ratio 42% Concentrate solid Spray dried powder rate: @3%moisture. 250kg per hour Annual production: based on 270 days/6500 hours production time 1625tonnes An agglomerator
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
Fig 8. 2: Moden Production of Instant Coffee Packing Roasting and Grinding Extraction Concentratio eaning and Blending courtesy of Niro Atomiser
vi a E x 6 f. 8 2 E 3 tj E 3 .L, iE Y .E! 6 4 s I: 4 12 I: z a * e E wh U .9 cg "! 2 B In .- I 5 200
FREEZE-DRYING OF COFFEE Whilst it may be pertinent to describe the principles of freeze-drying coffee, it is a high capital investment project, spearheaded originally by General Foods Corp in the USA in 1964. Subsequently, production was extended in he States and Nestle entered the field and developed the process in Brazil, in the USA. whilst it i as a premium priced product, on account of the relatively high operating costs compared with spray dried coffee, freeze-dried coffee will undoubtedly hold its share of the market but it is not an area into which many newcomers may venture, as the market has been cultivated by the multi-nationals who were in from the beginning and have dominated the trade by expensive advertising and marketing devices which only massive organisations can sustain Technically, the first stages of the processes are similar to those applying to spray drying: blending, roasting, extracting and concentration. At this point the 30 percent solids extract is sometimes freeze-concentrated to 40 percent solids, and then frozen to about minus 50"C. The product is hen granulated, transferred into trays and dried in a vacuum chamber in an 10 hour cycle to about 2 percent moisture. End temperatures in the granules range from 37 to 40C A two stage compressor is needed to maintain a temperature of minus 50C in the condenser coils of the freeze dryer, and either ammonia or Freon is used as a ref A standard batch chamber dryer has a tray space of 93sq m and requires a 66ton two stage recirculating installation to operate it. Most commercial units operating on the batch system have at least 4 chambers of 93sq m in service, which today could involve a capital outlay of some $3m for equipment alone, not including installation. This is only a modest percentage of the total investment involved. Some plants are completely automatic, adding considerably to the investment cost but not always saving much on the operating costs per kg of coffee produced PACKAGING This is invariably in retail or catering glass packs, hermetically sealed and nitrogen-flushed, as the product is extremely hygroscopic
