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



almost an all-year job, maintenance of cool storage to reduce spoilage 

 is important. 



Thorough washing is the first step in the preparation of potatoes. 

 This operation can be carried out by running them through a revolv- 

 ing corrugated-drum or squirrel-cage washer equipped with sprays. 

 Following washing, grading to size should be performed if abrasion 

 or radiant-heat peeling is used, since grading speeds up the peeling 

 operation and reduces waste. With lye or brine peeling, grading to 

 size is less important. 



Trimming is necessary after the peeling operation to remove the 

 eyes and black spots or unsound or damaged portions that remain 

 after the product has passed through the peeling machines. The to- 

 tal waste from peeling and trimming varies with the grade and size 

 of the tubers, the peeling method used, and the care exercised in peel- 

 ing and trimming. In commercial plants this waste is rarely lower 

 than 15 percent, and may rise to 30 or even 40 percent if the raw 

 material is inferior or the operation is conducted carelessly. With 

 abrasive peeling the average over-all loss is about 23 percent and the 

 range 18 to 27 percent. With lye, brine, or heat peeling, the losses 

 may be considerably less — as low as 12 percent. 



The peeled and trimmed potatoes pass to mechanical cutters where 

 they are cut into slices, cubes, or strips (julienne style) in accord- 

 ance with the form desired. (See p. 34.) 



After being cut the potatoes proceed to a washer where the loose 

 starch is removed. This operation is then followed by blanching. 

 If delay between cutting and blanching is unavoidable, the cut ma- 

 terial must be held under potable cold water or a clean 2 percent salt 

 solution. This procedure will protect the cut product from discol- 

 oration as the result of enzymatic oxidation. The prepared material 

 should not be held for more than 1 hour before blanching. If the 

 potatoes are to be riced, the peeled and trimmed potatoes can be 

 quartered or sliced and then blanched. (See table 21.) 



After being blanched, the material should be sprayed again with 

 clean water in order to remove loose starch that might cause the pieces 

 to stick together during dehydration. Delays between blanching and 

 dehydration should be avoided. In any case, the material should not 

 be held longer than 1 hour. Quartered potatoes that are to be riced 

 are exposed to live steam until cooked, usually for 20 to 25 minutes. 

 After this operation and while still hot, they are passed through a 

 mechanical ricer directly to the drying trays. 



Information on the moisture content of potatoes and on the maxi- 

 mum moisture content permitted by Government specifications for de- 

 hydrated potatoes is given in table 22. The drying ratio and drying 

 yield are shown in table 23. Tables 24 and 25 contain information on 

 dehydration. (See pp. 184-187.) 



Tin cans have been replaced to some extent by 5-gallon square 

 cartons as containers for dehydrated potatoes. Dehydrators will re- 

 quire between 250 and 380 five-gallon cans or cartons for every 10 tons 

 of raw untrimmed potatoes that are to be dehydrated (table 26). De- 

 hydrated potatoes are moderately sensitive to heat, being less suscep- 

 tible than carrots and more so than sweetpotatoes. In 1921 Gore 

 and Rutledge (18) reported that dried potatoes containing 6.3 to 6.6 



