Elements of the theory and practice of cookery

1 The sweet potato is a true root, but from its resemblance to a tuber is called a tuberous root. It differs from a white potato chiefly in containing sugar. 62 THEORY AND PRACTICE OF COOKERY D. Add a drop or two of iodine solution to the white substance obtained from the potato. What do you think it is? Test a slice of potato for starch. COMPOSITION OF POTATO AS SHOWN BY ROUGH ANALYSIS 1. Plant fibre (partly cellulose). Similar to fibre of wood. Forms walls of cells, or lit- tle divisions, in the potato. Too tough to be digested ; there- fore of little food value. 2. Water. About 75 per cent of the weight of the potato. Fills cells. 3. Starch. White insoluble powder The chief food- floating in water in cells ; with boiling water forms stuff in pota- toes. a jellylike paste. Potatoes also contain : 4. Potash salts and other m i n e r a 1 matter. 5. Other substa food value. Lying mostly just beneath the skin. nces in such small quantities as to be of little 111. To find out how much water a potato contains, pare and weigh it. Lay it in a warm, dry place, weighing it every day until it ceases to lose weight by evaporation FUEL FOODS: SOME STARCHY PLANTS 63 of its moisture. Compare the final weight with what it weighed at first. The difference between these shows how much water the potato contained. To show mineral matter in potatoes, heat a bit of potato in a crucible or evaporating dish over a Bunsen burner till only gray ashes are left. 112. Experiment to show the relation between the sprouting of a potato and its composition. — Let a potato lie in a dark, warm place until it sprouts. Bring it to the light from time to time and ob- serve the growth of the sprouts, also any change in the size of the potato. What do you think the sprouts feed on? Would a sprouted potato be as nutritious as an unsprouted one ? 113. Growing and harvesting. — Potatoes are grown from cuttings, not from seed, each piece planted being cut so that it has two or more eyes. Why not leave one eye only ? They are planted in April and May, and harvested mainly in early autumn. 114. How to choose and keep potatoes. — The tuber is a storehouse of starch /or the nourishment of the young shoot. In potatoes dug too early the starch is immature or un- ripe. In those kept too long after digging the starch has been partly changed to gum, a substance more ser- viceable than starch to the growing plant, but not so nutritious for man. Potatoes are best (fullest of starch) in the fall and win- ter. Select those regular in shape, of medium size, and with smooth skin. A bushel of very large potatoes gives the purchaser less than a bushel of smaller ones, which pack more closely. Green bitter spots are caused by the potatoes being grown too near the surface of the ground. Keep them in a cool, dry place. If sprouts appear pick them off. 64 THEORY AND PRACTICE OF COOKERY 115. Economy in paring and cooking potatoes. — Is the skin of a potato thick in proportion to the eatable part ? Do we need to take off a thick paring ?