Starch (amylum) is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. All green plants produces these polysaccharides as an energy store. Starch is found in large amounts and processed most typically from grains (corn or maize, wheat, rye, barley), rice, cassava, and potato.
Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin.
Starch is manufactured to produce many of the sugars and byproducts used in processed foods. Dissolving starch in warm water produces wheat paste that can be used as a thickening, stiffening or gluing agent and in industrial applications such as binder, strength, printability, and texture in the papermaking process.
Starch molecules arrange themselves in the plant in semi-crystalline granules. Each plant species has a unique starch granular size and structure. Starch becomes soluble in water when heated. When heated, the granules swell and burst, the semi-crystalline structure is lost and the smaller amylose molecules start leaching out of the granule, forming a network that holds water and increases the mixture's viscosity. This process is called starch gelatinization. During cooking, the starch becomes a paste and increases further in viscosity.