Oat Hulls for New Zealand and Australia. Oat hulls are the outer shell layer of the oat, inedible and normally removed from the oat, when used for brewing the hulls improve the filter bed of the mash to decrease the likelihood of a stuck mash. Oat hulls are non-fermentable, and provide bulk helping prevent the mash from settling and becoming stuck during the sparge. Hulls are generally used when making wheat or rye beers. Please note: Gladfield does not produce this product.