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