6 
BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE. 
ters is in the outer layers, this waste appears more important than is 
generally realized. The mechanical potato parers now available 
usually remove the skin with much less loss of edible material, and 
they have the further advantage of saving time for all but very skill- 
ful workers. There are a number of kinds on the market, which 
either pare the potatoes in much the same way as is done by hand or 
else rub off the skin. 
The carbohydrates stored in the potato form 18.4 per cent of the 
edible portion. Most of this is starch, though there are also small 
quantities of soluble carbohydrates or sugars. Young tubers have a 
larger proportion of sugars and less starch than mature potatoes. If 
the tuber lies in the ground the starch content increases for a time, 
but when it begins to sprout part of the starch is converted by a 
ferment in the tuber into soluble glucose. Thus, both young or early 
potatoes and old ones have a 
smaller proportion of starch 
and more soluble sugars 
than well-grown but still 
fresh tubers. 
Less than 0.5 per cent of 
the carbohydrates is cellu- 
lose, yet one sometimes 
hears the statement that 
potatoes are indigestible on 
account of the large quanti- 
ties of cellulose which they 
contain. In reality there is 
no more cellulose in the po- 
tato than occurs in most of the cereals and in other vegetable foods, 
and so such a criticism of the potato has no warrant in fact. 
Besides the carbohydrates mentioned, potatoes also contain a little 
pectose, the French investigators quoted above reporting the pres- 
ence of 0.2 to 0.4 per cent. Pectose, which is so important in jelly 
making when it occurs in quantity, as in fruits, is believed to have 
practically the same food value as other carbohydrates. 
Fat appears in such small quantities in potatoes that it may be 
practically neglected in discussing their food value, especially as the 
greater part occurs in a waxlike form in the inedible skin. 
The protein bodies are rather small in quantity, as compared with 
those of cereals and such vegetables as peas and beans, and only about 
80 per cent of the total amount present is available protein; that is, 
protein in a form which can be used for the building and repair of 
body tissues. This means that a pound of potatoes furnishes only 
about 0.2 of an ounce of available protein and emphasizes the state- 
loss //v 
or whole por/iro 
LOSS //V 
C/}/?£LFSSP£EL/HG: 
ASOVT OM£ F/FTrt 
or w/so££- /=>oz4ro 
Loss of weight in peeling potatoes. 
