Beta Glucanase is an enzyme that hydrolyzes β-glucans. The most important β-glucanases for brewing are those that break down the β-glucans located in the cell walls of the barley endosperm. See beta-glucans. High levels of β-glucans in brewing raw materials are to be avoided as they can cause problems, particularly in wort production and beer filtration. β-Glucanases are important in that they are needed to break down the complex β-glucan molecules to smaller units. There is a wide range of such enzymes, differing in the specific bonds that are broken.

The most important such enzyme in barley is endo-β→3, 1→4-glucanase (sometimes called endo-barley-β-glucanase) which potentiates the hydrolysis of a β1→4 linkage adjacent to a β1→3 linkage, thereby leading to a rapid diminution in the viscosity of β-glucan solutions. The enzyme is essentially absent in raw barley, but is synthesized during germination and functions during malt modification to remove the problematic β-glucans. The enzyme is extremely sensitive to heat and if the enzyme is required in the brewhouse grist, for example to deal with residual β-glucan in poorly modified grain or adjuncts rich in β-glucan such as raw, roasted, torrefied, or flaked barley or oats, then the green malt must be kilned at a lower onset temperature with progressive ramping to a non- excessive final curing temperature. Furthermore, mashing needs to commence at a reduced temperature (e.g., 40°C–50°C or 104°F–122°F) if the β-glucanase is to function at that stage. Alternatively, more heat-tolerant microbial β-glucanases can be added to the mash. These include the enzyme from Bacillus subtilis, whose specificity is very similar to that from malt, or glucanases derived from fungi such as Aspergillus, Trichoderma, or Penicillium, which comprise mixtures of enzymes with different specificity, including endo- and exo- β1-3- and β1-4-glucanases. As a consequence they are much more comprehensive in their removal of glucan.

Yeast cells can be “opened” by the action of lytic enzyme, which is β1-3 glucanase derived from snails that degrades that particular glucan, a key structural feature of the yeast cell wall.