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



Onions are usually received in sacks containing up to 100 pounds, 

 and to prevent overheating are stacked until used. Handling is much 

 more simple for this product than for most vegetables, because blanch- 

 ing is not required. The onions are thoroughly washed and cleaned 

 to remove soil and foreign material ; then the outer, discolored layers 

 are removed, after which the root base and top are cut off. They 

 should be cut mechanically into slices or shreds ranging from one- 

 eighth to one-fourth inch thick. In pilot-plant operations, peeling 

 and trimming losses have varied from 6 to 15 percent. 



Government purchase specifications for dehydrated onions do not 

 require blanching of the raw material (table 21). There is evidence 

 that storage life of the dried product is prolonged by blanching but if 

 onions are blanched they may fail to meet existing specifications, since 

 the appearance of the blanched product is less attractive than that of 

 the unblanched. Prolonged blanching may cause a marked loss of 

 pungency. The cut material should not be held longer than 1 hour 

 before blanching or dehydration. Information on the moisture con- 

 tent of onions and on the maximum moisture content permitted by 

 Government specifications for dried onions is given in table 22. The 

 drying ratio and drying yield are shown in table 23. Tables 24 and 25 

 contain information on clehvdration, and table 26 on packaging (see 

 pp. 184-188). 



Government specifications limit the moisture content of onion flakes 

 and slices to 4 percent and, in practice, flakes are packed at 3.5 percent 

 moisture content. Onion powder should have an even lower moisture 

 content, in order to prevent lumping. Dried onions are fragile ; this 

 fact should be kept in mind during handling in order to keep the fines 

 low. Onion powder and flakes will absorb moisture in air having a 

 relative humidity about 25 percent and in the room where onions are 

 ground the atmosphere must be air-conditioned to 30 percent or less 

 for the best results. Export shipments for the armed forces are made 

 in hermetically sealed 5-gallon, square tin cans. For domestic ship- 

 ments cartons having double waxed-paper liners, or cartons made of 

 laminated material, including a layer of lead foil, are also used. 



Dehydrated onions are more sensitive to heat than are potatoes, 

 which occupy a middle position among dried vegetables in regard to 

 stability. Experience has shown that too high temperature or too 

 long exposure to a lower temperature causes a brownish color. 



Dried onions in both the powdered and the rehydrated flake or 

 slice form are used largely as seasoning agents. Kehydrated flakes or 

 slices can be used in salads or as seasoning in soups or other vegetable 

 mixtures and in other recipes that require raw onions, or they can 

 be stewed and seasoned as a vegetable dish. Soaking at room temper- 

 ature or in a refrigerator in a minimum amount of water (enough to 

 insure wetting of all pieces) is the most suitable method of rehydration, 

 and a minimum of 2 hours is required. Unblanched onion pieces will 

 take up enough water to make them turgid and crisp in that length 

 of time. There is considerable transfer of pungent flavor to the water 

 during soaking, and, in the producer's directions for use, the sugges- 

 tion should be made that unabsorbed water be used in soup stock or 

 meat gravy. 



Rate and completeness of rehydration can be determined by soaking 

 the product in seven to eight times its weight of water, draining, and 



