The first division of combustible compounds is called carbonaceous because they all contain carbon; or heat-producing, because by their burning they generate heat. They consist of starch, sugar, fats and oils, gum, and the softer fibres of plants. They are found in vegetables, cereals, fruits, milk, eggs, and the fat of meat.
Starch is one of the most important of vegetable foods; it is found in grains, seeds, and roots, and in the pith and bark of plants. When pure, it is a snow-white, glistening powder. It consists of exceedingly minute grains, varying in size and shape in the different kinds of starch. These grains are covered with an outer skin which is insoluble and unchanged by cold water; but in boiling, this membrane bursts and the interior of each grain dissolves in the water, forming a thick, gummy solution. When cool, it stiffens into a kind of pasty mass.
Starchy food is very unwholesome unless properly cooked. It must be mixed with a sufficient amount of liquid, and subjected to a great degree of heat, that the grains may swell and burst. This liquid is sometimes supplied by the boiling water in which certain starchy foods are cooked; and sometimes by fat which melts with the heat, as in pastry, or by boiling fat, as in anything fried. When flour or starchy food is mixed with fat, it should be finely and evenly mixed, that the fat may penetrate every part of the flour, or else it will cake, and all the grains will not burst. Anything that helps to make pastry lighter and the fat more evenly distributed, causes the starch grains to burst equally, and makes such food more wholesome.
Vegetables should be put into boiling water to burst the starch cells, and set free the confined air, of which there is a great deal in many kinds. They should be taken up as soon as they are soft, as they absorb water after the grains are fully burst.
Starch in its uncooked, insoluble state is not digested by the human stomach. Seeds and fruits which consist of starch, especially if it be combined with oil, as in many nuts, if eaten uncooked, are very difficult to digest.
All starchy articles of food should be masticated thoroughly, and mixed with the saliva. It is more necessary to chew bread and potatoes well than meat. Starch is changed by various means into sugar. If an acid be added to it in a watery solu-tion, and boiled, it becomes clear and transparent, and after a time all the starch disappears, and sugar takes its place. The same change is caused by the saliva, and during digestion the starch is all changed into sugar, so that none of it is found in the fluids and secretions of the body. This is easily seen by chewing pure starch; after a while it will become sweet.
Starch contains no albuminous substances, and therefore cannot supply any of the materials of which our bodies are formed. But it is the source of the warmth of our bodies, and the strength we exert. Taken alone, it would be useless as an article of food. It must have the addition of albuminoid and fatty substances, like milk or meat.
Starch is prepared by grinding some vegetable matter that contains it in abundance, and mixing it with cold water. The water is strained and allowed to stand; the starch settles at the bottom, and is then dried and powdered. Cornstarch is obtained from Indian corn, by a chemical process. The glutinous, oily elements are freed from the seed by alkaline solutions, and the starchy parts are ground and dried. Sago is starch from the pith of a species of palm-tree. Tapioca is from the root of a species of the cassava plant of South America. It is a coarsely granulated substance. Cassava, or mandioc, is a more finely granulated form of the same root. Arrowroot is from the rhizoma, or rootstalk, of a West Indian plant. The natives use the roots of a species of the plant in extracting the poison of arrows; hence the name.