Base Malt is malt that has enough enzymatic activity, notably diastatic power, to ensure that starch conversion occurs during mashing. It usually accounts for the largest percentage of malt in a beer recipe (anywhere from 60% to 100%). The remaining percentage may be made up of specialty malts, unmalted grains, or adjuncts that may not have enough enzymes to convert their own starches to sugars during mashing. In essence, the base malt provides for the production of fermentable sugars and free amino nitrogen for the yeast to consume during fermentation. The entire grist bill represents the substrate but the base malt provides both substrate and enzymes.

When selecting a base malt for a given recipe, brewers are interested in several factors, some of which are included in a standard malt analysis sheet: moisture content, potential extract, color, protein content, and diastatic power. Brewers also want to know the barley (or other grain) variety, place of origin, and type.

Most often, but not always, base malt is a two-row or six-row pilsner or pale ale malt. For example, a pale ale recipe may comprise 85% base malt (pilsner or pale ale) and 15% specialty malt. However, in German weissbier, wheat is the base malt, sometimes up to 60%, with pilsner malt making up the remaining balance. Some other specialty beer may use other base malts. Traditional German märzenbier can be made from 100% Munich malt, which concentrates that malt’s toffee-like flavors.