Pentose is a monosaccharide sugar composed of five carbohydrate atoms. In barley and other grains, pentose occurs naturally as the monomer of polymers called pentosans, non-starchy polysaccharides found in the cell walls of the grain endosperm. The principal pentoses are xylose and arabinose; hence, the pentosans are called arabinoxylans. Pentosans are also the main building blocks of barley husks. Pentosan amounts to merely 3% to 4% of all of the carbohydrates in barley, and about 20% of pentosans are hydrolyzed and degraded into pentose during malting. As sugars, therefore, pentosans play only a minor role in beer making, although their survival into beer is said by some to benefit foam stability. They also may be claimed to represent soluble fiber, with possible health benefits.