Maltose

Maltose is a disaccharide built from two D-glucose units; splitting it by hydrolysis gives two molecules of glucose. It is found to a limited extent in sprouting grain, and it forms when starch or glycogen is partly broken down. During beer making it is released from starch, which is the reason it is called malt sugar.

It is a modest sweetener, about 30% as sweet as sucrose. The same chemistry page places it beside two other disaccharides: lactose, the milk sugar made of galactose and glucose, which is only about one-sixth as sweet as sucrose, and sucrose itself, the table sugar made of glucose and fructose. Of the three, maltose is the one most closely tied to grain, since it appears when sprouting grain or starch is broken down. Its gentle sweetness and its link to grain and malt make it a useful term for understanding how starch turns into sugar.