Principles of cooking

(Farmers' Bulletin, No. 389, Dept. of Agriculture, U.S. Dept. of Agriculture.) called cellulose. Each cell consists of a network of protoplasm which incloses granules of starch or sugar, mineral matter, and water, and is surrounded by a wall of cellulose. Cellulose is of the same composition as starch, but is unlike it in structure and in appearance; heat and the digestive juices have not the same effect on it that they have on starch. When cellulose grows old, it becomes tough and woody. The human stomach cannot digest cellulose; and as it incloses the starch and other sub- stances that can be digested if the digestive juices can reach them, these cell walls must be softened by cooking so as to set free the inclosed starch, sugar, mineral matter, and protein. | When the cells contain much starch, moisture and heat cause the starch grains to swell and burst the walls of cellulose which inclose them. Some foods, like potatoes, WA ONG MWA Wa an e Ag Yt 1_S. y= NE wy if Nay CHANGES IN STARCH CELLS IN COOKING. A, cells of a raw potato with starch grains in natural condition; b, cells in a partially cooked potato; c, cells in a thoroughly boiled potato. (From Farmers’ Bulletin No. 389, contain enough water to cause the starch to swell when the water turns to steam, and this causes the bursting of the cell wall. Some foods, like rice, corn, and wheat, are cooked in water; and the starch absorbs water during cooking. When starch is cooked we sometimes say it is gelatinized, and the starch in different foods cooks or gelatinizes at different temperatures. The starch in oats gel- atinizes at 185° F., corn at 167° F., potatoes at 149° F., other cereals at 176° F. Some foods, like lettuce, celery, — tomatoes, onions, contain so little starch that it is not necessary to cook them, because we eat them, not for the starch in them, but for the cellulose, mineral matter, and acids which they contain, and which have important uses in the body. ee a a In some foods the cellulose is so tough that it must be softened, even though the food does not contain much starch. The greater the amount of cellulose in a food the longer time it takes to cook it. Some foods, like old beets _and carrots, are so tough that it is a waste of fuel to try to cook them. Recipe for Baked Potatoes. — Select smooth, mediumsized potatoes. Wash clean, using a brush to scrub and a knife to remove the specks and blemishes. Place on the grate of an oven of moderate temperature and gradually increase the heat. Bake until soft, about 40 minutes. Break or pierce the skin to allow the steam to escape, and serve in an uncovered dish. A moderate oven is needed in starting to allow the heat to penetrate to the inside of the potato. If the heat is too intense at first, it forms a hard crust on the outside, keeps out the heat, and prevents the potato from cooking evenly throughout. If the steam is allowed to remain in the potato, it condenses and the potato will be soggy. ‘ With what would you serve baked potatoes? At what meal? Potatoes are the most important of all vegetable foods, except wheat, because they are the most extensively used. They contain, after they are pared for cooking : — Water Starch Cellulose Protein Fat Mineral Matter 78.3% 18% 1% 1% 0.1% 1% Note. — Experiments to show composition of potato will be given in Chapter V, page 74, but the teacher may well give the starch test here. A solution of iodine turns starch blue, and pupils may test various foods to detect the presence of starch. The most important principles involved in the baking of potatoes are those which govern the cooking of starch and the softening of cellulose.