If you have a severe intolerance to gluten, or celiac disease that requires a gluten-free diet, then you should be concerned about gluten in yeast. Yeast is a micro-organism that is classified as a fungus and so, by itself, does not contain any gluten, a protein found in foods such as wheat, barley, and rye. The way in which yeast is cultivated and the medium used to distribute yeast, however, can be cause for concern regarding gluten in yeast. Yeast that is cultivated using barley, for example, can contain gluten and should be avoided by anyone on a gluten-free diet.
The issue of gluten in yeast may, initially, seem rather absurd. This is because yeast is a well-known micro-organism that does not, on its own, contain any of the proteins known as gluten. Someone who understands what yeast is, but not necessarily how it is developed or packaged for commercial sale and consumption, might then assume that all yeast bought in a store is innately gluten-free. While the actual yeast itself is gluten-free, there is the potential for gluten in yeast that is sold in a packet or container, depending on how the yeast was cultivated.
Brewer’s yeast, for example, which is often used in making beer or alcohol, frequently contains trace amounts of barley or wheat that may contain gluten. This means that someone may be exposed to gluten in yeast that was cultivated in this way. Though this would likely be a very small amount of gluten, those with celiac disease or severe gluten intolerance may have a negative reaction to any quantity of gluten. Other types of yeast may be cultivated through the use of beet sugar, which means that there is no concern for gluten in yeast of this kind.
Most types of yeast that are free of gluten are marked appropriately to avoid concern over gluten in yeast that is gluten-free. Yeast is often used in baking, by allowing yeast in dough to consume sugars in that dough and create carbon dioxide, which is then trapped in pockets of gluten that make the dough rise. Since someone worried about gluten in yeast is unlikely to use other products in bread that would produce gluten, he or she typically needs to find other ways to make the bread capture gas released by the yeast. Replacement ingredients such as xanthan gum can be used to make gluten-free bread that still rises in a way fairly comparable to bread with gluten in it.