Guinness, a popular Irish dry stout, does contain gluten. In fact, the majority of beers produced worldwide contain gluten from the barley used in their manufacture.
Gluten is a protein found in many grains, such as wheat, barley and rye. Sufferers of gluten intolerance and celiac disease often find it difficult to avoid because of how pervasive these grains are. Although the vast majority of beers include malted barley and other grains that contain gluten, some breweries produce beer using sorghum, a gluten-free grain, in place of barley. As of 2014, the most widely available gluten-free beer is RedBridge, a beer produced by Anheuser-Busch. Many craft breweries, such as Dogfish, also offer gluten-free beers.