POTATOES AND OTHER STARCHY ROOTS AS FOOD. 19 
The proportion of total sweet potato 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 c&ne 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 the}^ 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 U. S. Dept. Agr., Farmers' Buls. 324 ; 548. 
