The Oxford Companion to Beer definition of
is devoid of proteinaceous material, derived from certain cereals, that can cause an immune reaction in the small intestine. People with Celiac disease cannot properly digest these proteins, and severe gastric disturbance can result from their consumption. “Gluten” is a word often used generically for storage proteins in plant seeds and more specifically the proteins are called gliadin in wheat, hordein in barley, and secalin in rye. They contain certain sequences of 10 to 20 amino acids that are resistant to attack by proteinases in the digestive tract and which induce damage in the small intestine. Oats are less problematic.
There has been much debate about the magnitude of the problem that regular beer presents, in view of the fact that there is extensive protein degradation and modification during malting and brewing. Nonetheless most brewers err on the side of caution and recommend that celiac patients do not consume “regular” beer, even those produced with sizeable quantities of adjuncts such as corn and rice.