Alpha conversion (gelatinization of starch)

Alpha conversion (α化, arufaka), also known as gelatinization, is the chemical change that occurs when raw starch in rice (mainly β-starch) is heated with water. In this process, the starch swells and becomes paste-like, which makes it easier for enzymes, particularly amylase, to break it down. Alpha conversion is a very important step in sake brewing: it allows sugars to be produced, and these sugars support fermentation by yeast. Because the rice starch processed in this way forms the basis of sake's flavor and alcohol, brewers need to manage this stage carefully.