Gelatinization in cooking refers to the gelatinization of starch in which starch granules swell when heated in the presence of water. Prolonged heat and stirring (or pressure such as in making popcorn) is necessary to completely dissolve the starch granules. This process can be applied to create many foods including popcorn, pastries, roux sauce and custards.
Gelatinization can also refer to, more generally, as a thickening of a liquid. Gelatinization temperatures depend on the type of starch, the amount of water, the number of damaged starch granules, pH, and other recipe ingredients (including sugar, salt and fat). The range for gelatinization is from 55-85 degrees Celsius.