From How to Brew by John Palmer: "Not an adjunct per se, the hulls of oats and rice are not fermentable, but they can be useful in the mash. The hulls provide bulk and help prevent the mash from settling and becoming stuck during the sparge. This can be very helpful when making wheat or rye beers with a low percentage of barley malt and barley husks. Use 2 - 4 quarts of oat or rice hulls for 6 - 10 lbs. of wheat if doing an all-wheat beer. Rinse thoroughly before using."