Katie Ziewacz, age 13, of Bowling Green, Ohio, for her question:
WHAT IS STARCH?
Starch is a powdery substance that is found in the living cells of green plants. It can be found in the seeds of corn, wheat, rice and beans and in the stems, roots and underground roots or tubers of the potato, arrowroot or tapioca plants.
Starch is a carbohydrate, one of the most important foods. Starchy foods are an important source of energy for both man and animals. When starch is digested in the body, energy is directly obtained from it.
During a green plants food making process, called photosynthesis, the energy of sunlight changes water and carbon dioxide into glucose and oxygen. Plant cells can quickly convert the glucose into starch.
Tiny starch grains are formed in most green leaves during the day. At night, the starch is converted back to sugars, which then move to the root, stem, seeds, fruit and other parts of the plant. The sugar may be used for growth, or stored again as starch.
When starchy 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 cooking of some foods, the starch may change into other substances. During baking, for example, a small amount of starch becomes the sugar maltose.
Chemists use iodine 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.
Industry manufactures more than 5 billion pounds of starch each year in the United States. About half is sold as starch and dextrin, and 1.5 billion pounds are converted into starch syrup.
Most starch is used to size or stiffen weaving yarn and to finish the cloth. Starch also gives high quality paper strength and a smooth, glossy finish. 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 part of the inside is removed. The kernel fragments are next 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.
Arrowroot and tapioca starch may be produced by similar methods.
Wheat starch can be manufactured by mixing wheat flour into a dough. The starch is washed out of the sticky mass by a stream of water.
Rice starch is made by soaking the grain in an alkaline chemical, which dissolves the gluten but not the starch. The starch is then separated and washed.