Rice Hulls are the hard outer layers of grains of rice. During normal harvesting of rice, the shard-like hulls are a by-product that later find other uses. After extensive boiling and drying to remove flavors and color, rice hulls are often used in the fruit juice industry as an aid to filtration and pressing operations. In brewing, many craft brewers blend them into mash to ensure good wort flow through the mash (or lauter) bed.

Rice hulls are most often used during the production of beers with high percentages of nonbarley cereal-grain adjuncts such as wheat or rye. These grains have higher levels of protein and beta-glucan compared with barley and lack the husks that create needed porosity in a mash bed. Higher protein and beta-glucan levels increase wort viscosity, sometimes forcing the brewer to increase mash bed porosity artificially. Rice hulls are favored by brewers because they do not contribute flavor or color and do not break down in the mash; they remain stiff and act to “open up” the mash bed. Oat hulls are another option for increasing bed porosity or reducing wort viscosity. As craft brewers produce increasingly stronger beers, they use more malt in their mashes, and the depth of the mash beds increases accordingly. Greater bed depth also decreases wort flow, and once again rice hulls often come to the rescue. Some brewers, looking to push the limits of style and their brewing systems, have sought to use rice hulls to produce beers from grists of 100% hull-less wheat.

Rates of usage can vary with the percentage of adjunct grains, but in general, adding between 1% and 5% of total grist weight in rice hulls directly to the mash helps ensure better wort runoff rates and greater wort clarity.