David Gamez, age 12, of Keen, N.H., for his question:
WHAT EXACTLY IS STARCH?
Starch is a white, powdery material found in the living cells of green plants. It can be found in the seeds of corn, wheat, rice and beans and also in the stems, roots and tubers of potato, arrowroot or tapioca plants.
Starch is a carbohydrate and it is one of the most important food items. Starchy foods are an important source of energy for man and animals. When starch is digested in a person's body, energy is then directly obtained from it.
Starch, or flour that contains starch, is often used in cooking to thicken mixtures. The mixtures usually become pasty or jellylike. When starch foods such as rice or macaroni are cooked, the starch granules swell and absorb water.
Starch does not dissolve in water. Cooked starch is easily broken down in the body by digestive enzymes. But uncooked starch is too insoluble to be digested easily.
During the cooking of some foods, the starch may change into other substances. For example, during bread making a small amount of starch becomes the sugar called "maltose." Maltose is fermented by yeast and changed into carbon dioxide and alcohol. The carbon dioxide forms bubbles in the dough and makes it rise.
Iodine is used by chemists to test for the presence of starch in food. When a small amount of iodine is added to a starch solution, it becomes blue black.
Under the microscope, starch appears as tiny granules. Cornstarch granules are rounded, irregular polygons. Polygon means many sided.
Potato starch granules are oval with concentric rings and may be more than 100 microns in diameter. Rice starch has tiny granules about three microns in diameter.
Industry manufactures over 5 billion pounds of starch in the United States each year. About half of it is sold as dextrin, and about 1.5 billion pounds are converted into starch sugar.
Most of the starch manufactured is used to size or stiffen weaving yarn and to finish the cloth. Starch gives high quality paper strength and a smooth, glossy finish. And starches are also used in making pasteboard, corrugated board, plywood and wallboard.
To manufacture cornstarch, corn is soaked in warm water and sulfur dioxide for two days. The softened kernels are then torn apart and the "germ," or inside part, is removed. The kernel fragments are then ground and screened down to starch and gluten.
The starch is then filtered, washed, dried and packaged. Similar processes are used for starch from waxy maize and sorghum.
To make potato starch, the potatoes are washed and ground, and the starch is separated from potato fibers by screening. After further separation, the starch is washed and dried.