Page:Foods and their adulteration; origin, manufacture, and composition of food products; description of common adulterations, food standards, and national food laws and regulations (IA foodstheiradulte02wile).pdf/335

 portion of the country the sweet potato is often allowed to remain in the soil during the greater part of the winter, and, if the vines are removed, it keeps in excellent condition.

Yield and Composition of the Sweet Potato.—As has already been mentioned, there is a general resemblance, in so far as chemical and nutritive properties are concerned, between the sweet potato and the potato. The sweet potato is usually colored a yellowish tint, due to the distribution of more or less xanthophyll throughout its substance. The sweet potato also contains notable quantities of cane sugar, to which its name is due. It, however, contains large quantities of starch and fiber and small quantities of protein, resembling in this general manner the potato itself. The sweet potato has not been used in the United States for the making of alcohol. In the Azores great quantities of sweet potatoes are grown for this purpose, and make an alcohol of fine quality, which is used to a large extent in fortifying port wines. There are large areas in the United States, especially in the Southern States, where the sweet potato can be grown in great abundance. The experiments at the South Carolina station show that as high as 11,000 pounds of sweet potatoes can be grown per acre. The percentage of starch is markedly greater than in the white or Irish potato. In all cases over 20 percent of starch was obtained in the South Carolina sweet potatoes, and in one instance over 24 percent. As high as 2,600 pounds of starch were produced per acre.

In addition to starch, the sweet potato contains notable quantities of sugar, sometimes as high as six percent being present, so that the total fermentable matter in the sweet potato may be reckoned at the minimum at 25 percent. A bushel of sweet potatoes weighs 55 pounds, and one-quarter of this is fermentable matter, or nearly 14 pounds. This would yield, approximately, 7 pounds, or a little over one gallon of 95 percent alcohol. It may be fairly stated, therefore, in a general way, that a bushel of sweet potatoes will yield one gallon of industrial alcohol. The average yield of sweet potatoes, of course, is very much less than that given in the South Carolina reports, where heavy fertilization was practised. On plots to which no fertilizer was added the yield was about 8,000 pounds of sweet potatoes per acre, yielding in round numbers 1,900 pounds of starch. The quantity of sugar in the 8,000 pounds is about 350 pounds, which, added to the starch, makes 2,250 pounds of fermentable matter per acre. This will yield 1,125 pounds of industrial alcohol of 95 percent strength, or approximately 160 gallons per acre.

The yield of sweet potatoes in the above computation must be regarded as exceptionally high. A safer calculation will be based upon the yield of 100 bushels of sweet potatoes per acre, a little above the average of the yield of the potato, or a total of 5,500 pounds per acre. One-quarter of this amount is fermentable matter—about 1,400 pounds—which would yield, approxi-