4 MISC. PUBLICATION 5 4 0, U. S. DEPT. OF AGRICULTURE 



He may discover that a crop grown in a given area requires different 

 treatment from that required by the same crop, and even by the same 

 variety, grown under different conditions. He should assure himself 

 that the crop or crops to be dehydrated are high in original nutritive 

 and other quality factors. 



Large quantities of heat, power, and pure water are required for the 

 operation of a dehydration plant and these should be available at a 

 reasonable price. If steam is used as a source of heat, the type of fuel is 

 relatively unimportant. Heat consumption is lower with direct heat 

 and this requires the use of gas or oil fuel, preferably the former. 



Difficulty in disposing of wastes from the preparation line, including 

 the wash water, has resulted in the closing of some plants. The 

 starch from potato plant wash waters tends to settle rapidly in sewer 

 lines and may result in clogging unless a heavy flow of water is main- 

 tained. The large tonnages of solid wastes must also be disposed of in 

 such manner as to avoid the creation of a nuisance. Attempts have 

 been made to recover the starch from potato plants in a salable form. 

 The low value of the recovered crude starch makes the advisability of 

 this process somewhat doubtful. Plants using abrasive peeling offer 

 the best opportunity for this type of saving, because of the large peel- 

 ing losses in these plants. 



Plants drying onions or garlic must be located so that prevailing 

 winds carry the nuisance odors away from populated areas. On the 

 other hand, all dehydration plants should be located where odors from 

 other sources will not trouble them. The flavor of dried vegetables 

 may be damaged by absorption of such odors and the acceptability of 

 the product seriously impaired. 



PLANT LAY-OUT, EQUIPMENT, AND CAPITAL INVESTMENT 



A properly planned dehydration plant is not built around a particu- 

 lar piece of equipment or around a certain step in the process. The 

 different operations must be balanced, with no "bottlenecks." The 

 capacity of each piece of equipment should therefore be somewhat 

 flexible so that an operating balance can be obtained without seriously 

 impairing the efficiency of any part of the plant. Plants in the ca- 

 pacity range of 5 to 100 tons per day, unprepared basis, are discussed 

 here, and most of the statements are equally true for larger plants. 

 Figures 1 to 5 illustrate floor plans that are considered later in more 

 detail. Vegetable rather than fruit dehydration has been considered 

 chiefly in the preparation of these plans and in the discussion of plan- 

 ning. Many of the general statements also apply to the dehydration 

 of fruits. 



Each prospective dehydrator will have individual preferences con- 

 cerning many features of lay-out, construction, and operation. The 

 equipment, the lay-outs, and the operating steps outlined herein are 

 offered as constructive suggestions. Many important matters have 

 not been illustrated because custom tailoring is necessary in almost 

 every case. Those omitted include such operations as air desiccation, 

 grinding, storage of raw material or finished product under special 

 conditions, and numerous techniques still unproved on a commercial 

 scale. 



Plants much smaller than 25 tons per day are not usually in a com- 

 mercially competitive position unless they have some special advan- 

 tages, such as low-cost raw material or low-cost labor. Small plants, 



