Does yeast extract contain gluten?

Yeast extract is obtained by adding high amounts of salt to the culture of yeast cells in liquid medium, which literally causes cells to explode during the self-digestive process called autolysis. As such, yeast extract does not contain gluten.

However, despite generally being gluten-free, extracts from yeast cultures that were cultivated in barley or malt medium do contain gluten and need to have medium declared on the list of ingredients. According to Pocket Dictionary Acceptability of Foods & Food Ingredients for the Gluten-free Diet, celiac disease patients should avoid consuming yeast extract products when barley protein is listed as one of the ingredients.