20 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE. 
starch to sugar seems to be associated in a general way with seasonal 
changes in temperature. In sweet potatoes kept in cold storage (4° 
C.) there is a rapid disappearance of the starch and an accompanying 
increase in cane sugar. It is a matter of common experience that 
late in the season sweet potatoes are apt to deteriorate in quality and 
sometimes deyelop a disagreeable taste, especially if they haye been 
left in a cold place. The peculiar and characteristic flavor often 
noted is due to a fungus disease resembling dry rot. These unde- 
sirable changes may take place at any temperature below 50° F. To 
lessen the danger of shipping in cold weather, the southern sweet- 
potajo crop is usually sent north early in the autumn and stored near 
the retail market. 
In choosing sweet potatoes at the market, firm, fresh-looking ones 
should, of course, be preferred to the old and shriveled roots, and 
medium-sized, regular-shaped roots are more satisfactory than very 
large, very small, or irregular ones, for they cook 'more evenly, 
give less waste in paring, and are of better size to serve. Early in 
the season unripe sweet potatoes are sometimes marketed and may 
be recognized by cutting them; the flesh will soon turn dark green, 
whereas in the properly ripened roots it will not change color. 
COOKING. 
The changes which cooking makes in sweet potatoes are, in general, 
similar to those in white potatoes. One special point is generally 
noticeable — the longer the cooking is continued, the more moist does 
the roottbecome. This is probably because part of the starch is made 
soluble by the heat and then dissolved in the juice, while the cane 
sugar is sjnit up into simpler sugar. The very sweet southern 
varieties become so moist during baking that a sirup frequently oozes 
through the skin. 
There are man}^ different ways of preparing sweet potatoes for the 
table, the most common being simply boiling or baking. They are 
also fried, cooked with sugar and butter (when they are commonly 
called "candied"), used in making pies, like pumpkin or squash, or 
in other made dishes. 
DRIED AND CANNED SWEET POTATOES. 
Dried sweet potatoes were formerly prepared at home, and strings 
of them were hung from the rafters along with apples and other 
drying fruits and vegetables, but in these days of storage warehouses 
the custom has vary largely passed away. Special devices for evapo- 
rating sweet potatoes are on the market, and desiccated sweet pota- 
toes prepared in much the same way as desiccated white potatoes are 
