Potatoes are three fourths water. The solid matter consists largely of starch, with a small quantity of albumen and mineral matter, - chiefly potash salts held in solution in the juices. New potatoes, unless perfectly ripe, contain but little starch. In late summer and in autumn they are in their best condition. The amount of starch and albumen diminishes by keeping; and in spring, or when the potatoes begin to sprout, a part of the starch changes to gum, and this makes them sticky or waxy. Some of the water has evaporated, the membranes of the starch cells are dry and hard, and their value as food is diminished.

The amount of albumen in potatoes, though small, is more than that in any other of the moist vegetables. This, together with the fact that they are cheap and palatable, combine well with other foods, and are easily cultivated and kept, makes them a favorite vegetable food. But they have been greatly overrated, and should not be used alone, or in too great proportion. For they contain little heat-giving and flesh-forming material, and if they be depended upon mainly for sustenance, so large a bulk of them is required that the system is overtasked. They should be eaten with fat and meat to make perfect food.

As they contain starch, they must be cooked to be wholesome, and it is important not to lose any of their nutriment in the process of cooking. The most economical methods are baking, steaming, and boiling.

There is a difference of opinion as to whether potatoes should be pared or not pared before cooking. Many claim that the most nutritious part of the potato is the part in and near the skin, and that this is lost by paring. This is chiefly mineral matter, - silica, - an element needed by the hair and nails. The potash salts - the most valuable mineral constituent - are probably held in solution all through the juices, and if these juices are drawn out, no doubt much of the potash escapes.

Potatoes are often grown in soils not adapted to them, and are liable to disease. They belong to a poisonous family, and contain a bitter juice in and near the skin, which makes them indigestible. In cooking, this bitter principle is set free by the heat, and goes off with the steam, if they are opened or uncovered at once; if not, the potato absorbs it and becomes bitter. So, unless potatoes are sound and of the best quality, it is better to pare them before boiling, and to take off quite a thick paring, that all this juice may escape; and they should always be pared when they are to be cooked for people with weak digestion. If any of the potash salts are lost by paring, they can be supplied by the use of salads and other green vegetables and fruits. If not pared they should be thoroughly scrubbed, to remove all the earthy matter adhering to the skin. The skin of new potatoes is thin, and may be removed by scraping instead of paring.

Potatoes, when pared, turn brown if exposed to the air, and each should be covered with cold water as soon as pared, and should not be pared long before cooking. In the spring, when they are shrivelled and become gummy, soaking improves them by supplying the water they have lost and dissolving the gum, making them less sticky; but at any other time it is undesirable.

If we examine the potato under the microscope, we can understand why, in cooking, it should be put into boiling water rather than into cold. The starch is found throughout the potato, enclosed in cells the walls of which are thin membranes of an albuminous nature. Each cell contains ten or twelve grains, surrounded by a watery, albuminous juice. In cooking the potato, this juice becomes boiling hot, the starch grains absorb it and burst; so that each cell, which before cooking was wet and hard, is now filled with soft, mealy starch. If we begin to cook our potatoes by putting them into cold water, some of the gum and potash salts will be drawn out, and the starch will not begin to cook until the water boils. Hence, though the potatoes may look and taste well, no time is gained in cooking, and they must have lost some portion of their nutriment. But if put into freshly boiling water, this hardens the albuminous membranes of the outside cells, and prevents the escape of the juices. The water should boil gently, to prevent the potatoes from breaking. Salt should be added to slightly increase the density of the water and thus raise the boiling-point, and help retain the soluble matters. And lastly, and most important of all the steps in the process, the potatoes should be taken up the moment they are done, - that is, when a fork will pierce them easily. They should be drained at once, then shaken, and left uncovered, to let the water inside, which has not been absorbed by the starch, pass off as steam. If we cook them after the starch is all softened, the starch on the outside will absorb the bitter, boiling water in the kettle; after a time the potato will break up and partly dissolve, and we shall have a bitter, pasty, potato gruel, instead of a firm, but soft and mealy potato.