are quantitatively the major organic materials in nature. In polymeric form they comprise the main food reserves in living systems, e. g., starch in cereal endosperms and glycogen in yeast. They also have important structural roles, for example, they comprise the β-glucans and pentosans in the starchy endosperm cell walls of grain, the cellulose in the husk, and the glucans and mannans in the cell wall of yeast. Carbohydrates also form a part of the structure of some proteins (glycoproteins).

Carbohydrates have the general formula Cx(H2O)n; i.e., they are essentially “hydrates of carbon.” All sugars are carbohydrates, including the various sugars that are fermented by beer yeasts. Glucose, one of the simpler carbohydrates (sugars), has the formula C6H12O6. See glucose. Because it has six carbon atoms it is a hexose, from the Latin prefix hex for six, c. f., “hexagonal.” Sugars with five carbon atoms are called pentoses, from the Latin prefix pent for “five”—e.g., “pentagon”—and examples are xylose and arabinose. Polymers of sugar units containing five carbons are known as pentosans. Polymers of hexoses are called hexosans. Polymers of glucose are known as glucosans, or more commonly, glucans. Examples include starch but also the β-glucans from barley that can present major problems for brewers. See beta-glucans.

Carbohydrates can interact with amino acids to form flavorsome, low-molecular-weight and colored, high-molecular-weight materials (melanoidins) through the Maillard reaction that occurs under the high heat conditions of kilning and (to an extent) wort boiling.