12 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE. 



DRIED OR EVAPORATED POTATOES AND CANNED POTATOES. 



Potatoes are so valuable in the diet that many attempts have been 

 made to put them into a compact form in which they can be kept for 

 a long time. This is usually accomplished by drying, which pre- 

 serves them from decay and reduces their bulk. One of the oldest of 

 such preparations is that long used in Peru and known as " chunno," 

 made hj freezing, thawing, and drying, which reduces the potatoes 

 to about one-fourth of their original weight. There are a number of 

 evaporated or dried-potato preparations in American and European 

 markets, and although the method of preparation differs considerably 

 in the various brands, the main principle is the same, namely, driv- 

 ing off water and so preventing decay. The changes which we call 

 decay are caused mainly by the development of bacteria, molds, and 

 yeast. These can grow and reproduce only where there are favorable 

 conditions, of which the necessary ones are suitable food, moisture, 

 and warmth. Therefore, if the moisture is removed, their growth is 

 prevented or retarded. The fact that the bulk and weight of the 

 potatoes is reduced at the same time is an advantage, because dried 

 or evaporated foods are often useful for camping expeditions and 

 under other conditions where fresh potatoes can not be easily pro- 

 cured, storage space is at a premium, or transportation is difficult. 

 The chemical composition of such desiccated or evaporated potatoes 

 is practically that of the original tubers minus almost all the water. 

 (See Table I, p. 5.) Of course, if extreme heat is used in the prepa- 

 ration, part of the starch may be changed to dextrin, and there may 

 be other minor changes in the chemical composition. There is no 

 reason to suppose that drying involves a loss of nutritive material. 

 Its influence on such substances as vitamins (see p. 7) is not defi- 

 nitely known. 



The water content of various kinds of desiccated potatoes has been 

 found to range from 4.8 to 7.9 per cent and their total carbohydrates 

 from 77.9 to 80.6 per cent, showing their general composition to be 

 not very different from that of good white flour. Desiccated potatoes 

 are usually soaked in water before using, and the water which they 

 take up then and during cooking brings back their water content to 

 about that of ordinary potatoes. Their flavor and general character- 

 istics, however, are not quite those of good fresh potatoes. 



The canned potatoes found on the market are prepared for use in 

 camps or wherever it is not convenient to cook food. In composition 

 such goods do not differ much from similar potatoes freshly cooked. 



STORAGE— ITS EFFECT ON QUALITY. 



It is a fact of common experience that potatoes suffer more or less 

 change during storage, and this is a matter of importance from the 

 standpoint of household costs as well as of the table quantity of 



