POTATOES AND OTHER STARCHY ROOTS AS POOD. 19 



The proportion of total sweet potat6 discarded with the skin as 

 refuse is probably about the same as in white potatoes, 20 per cent. 

 The most noticeable differences between white and sweet potatoes are 

 in the carbohydrates and water. Sweet potatoes contain on an av- 

 erage about 9 per cent less water and 9 per cent more carbohydrates 

 than white potatoes. They also contain as little, or even less, protein ; 

 but the proportion of available protein is higher than in white po- 

 tatoes, being about 1.3 per cent. This advantage, however, is hardly 

 large enough to be of consequence, nor is the fact that they contain 

 a trifle more fat. 



More important than any of these differences is that in the nature 

 of the carbohydrates. Sweet potatoes contain a slightly larger pro- 

 portion of crude fiber than white, though the amount is no higher 

 than in most vegetables. As would be guessed from their flavor, they 

 contain considerable quantities of sugar, part of which is cane sugar 

 and part invert sugar or glucose. The proportion of sugar and 

 starch varies with the climate. The warmer the place in which the 

 plant is grown, the greater the proportion of food laid by in the form 

 of sugar. Tropical sweet potatoes sometimes contain almost equal 

 quantities of sugars and starch. Those grown in New Jersey, on the 

 other hand, probably do not average more than 5 or 6 per cent of 

 sugar, or about one-fifth of their total carbohydrates. 



After harvesting, sweet potatoes are put through a curing process 

 during which they lose moisture. Sweet-potato marketing and stor- 

 age are of special interest to the grower and shipper. The house- 

 keeper who wishes detailed information on the subject will find it 

 in earlier publications of the department, 1 as such questions have 

 received careful study by the department specialists. 



With respect to the storage of sweet potatoes in the home for 

 family use, it seems to be generally conceded that the best results are 

 obtained when the roots are kept in a dry, well-ventilated place, at a 

 moderately warm rather than a cold temperature. This would mean 

 that they should be stored in the pantry or some similar place rather 

 than in the cellar. In handling potatoes in the home care should be 

 taken not to bruise them, as when thus injured they are likely to 

 spoil. 



Little is accurately known about the chemical changes which take 

 place during storage. The chief one, however, is that of starch into 

 sugar. The most recent investigations indicate that after sweet 

 potatoes are first harvested there occurs a rapid transformation of 

 starch into cane sugar and reducing sugars, which is initially due to 

 internal rather than external causes. The somewhat slower and more 

 regular change which takes place during ordinary storage from 



1 TL S. Dept. Agr., Farmers' Buls. 324 ; 548. 



