Maltose is the principal sugar in wort and is derived from the breakdown of starch during the mashing process. Maltose is classed as a disaccharide and consists of two linked molecules of the basic “sugar” glucose. During the mashing process the natural enzymes present in the malt, and notably an enzyme called beta amylase, break down the starch present to create large quantities of maltose, approximately 40% of the total carbohydrate content of the wort. Optimizing maltose production during mashing is dependent primarily on temperature, with a range of 60°C–65°C (140°F–149°F) most suitable for beta amylase activity. Traditional single-infusion mashing is usually carried out within this temperature range. See infusion mash. During fermentation, the maltose present in the wort is transported into the yeast cell and broken down to its constituent glucose molecules before subsequent metabolism into cell components, alcohol and CO₂.

Maltose can also be added to the wort from starch sources other than malted barley. Maize, wheat, and other starch sources can be converted using mainly microbial enzymes to produce syrups containing a range of glucose polymers, with maltose the major component of syrups used in brewing. Special syrups containing high (70%) levels of maltose are known as “high-maltose syrups” and can be used to extend brewing capacity when mashing facilities are limited.

See also syrups.