DEHYDRATION PROCESSES

Press, Volume LXXX, Issue 24269, 29 May 1944, Page 3

DEHYDRATION PROCESSES

TREATMENT OF VEGETABLES ADDRESS BY DR. J. C. ANDREWS Vegetable dehydration processes were discussed by Dr. J. C. Andrews, vice president of the New Zealand Institute of Chemistry and deputychairman of the Council of Scientific and Industrial Research, in an address delivered at a recent meeting of the Canterbury branch of the Institute of Chemistry. Among the guests of the branch were' Sir Theodore Rigg and the Dominion Analyst (Mr R. L. Andrew). After explaining the advantages to be gained under war conditions by the dehydration of bulky foods, such as the saving of shipping space and tin containers, Dr. Andrews emphasised the importance of grading the vegetables to be processed. He said American , experiments with beetroot showed that there wa. a 29 per-cent, loss during preparation for dehydration with ungraded roots, while when three grades were treated separately the losses were 9 per cent, for large roots, 15' per cent, for medium-sized roots, and 28 per cent, for small. The raw product, he continued/ had to be of good quality, and if the vitamin content was not satisfactory the loss was less than in home cooking. Four main methods of peeling were described by Dr. Andrews—by means of abrasive rollers, hot caustic soda solution, a short flame treatment at 1200 degrees Centigrade, and by steam. The new plant at Riccarton would use the abrasive method.. After peeling, some vegetables, such as potatoes, would require to be dipped in brine or sulphite solution to prevent discolouration. Wastage occurred during the trimming process. Dr. Andrews showed samples to illustrate different trimming methods, carrots being diced, cabbages shredded, onions sliced, and , it. toes cut into strips. Before dehydration the vegetables were blenched in steam to inactivate enzymes, which had to be destroyed if satisfactory appearance, flavour, and vitamin content were to be obtained. Dehydration was carried out by subjecting the vegetables to hot air in tunnels through which trays were passed continuously. At Riccarton, said Dr. Andrews, a two-stage tunnel would be . used, a higher temperature being applied in the 'first stage, when much surface moisture was present. The water content was reduced to a low figure, from about 90 per cent, in the raw state to 7 per cent, in the case of potatoes, and to 4 per cent, for onions. It appeared that these figures were low enough for satisfactory storage, if the correct storage temperature was maintained. Scientific control of temperature, air flow, and humidity was essential for successful working of the plant. One interesting result of dehydration experiments had been the discovery of small holes in the usual tinned food container, said Ur. Andrews. Usually these holes were sealed by the liquid present _ with canned foods, the surface tension of the liquid being enough to prevent leakage. Better cans were required for dehydrated products, and American can -makers had been successful m meeting the demand foj them. The samples which Dr. Andrews showed were cooked during the lecture and tested by an interested audience.