Short answer: it is a protein that’s found in wheat, wheat variants, barley, and rye. These grains appear in many of the foods we eat.
But I am chagrined! It seems that I, a medical doctor, was destined to write the six pages in Gluten-Free Bread in Five Minutes a Day, called:
So what’s the problem with gluten? For whom? A wee bit of science
But my “wee bit of science” never told readers exactly what gluten is! So my apologies for that. Maybe I should ask Jimmy Kimmel if I can be in his “What is Gluten? video (not to single out folks from Los Angeles, but they don’t seem to know, and I didn’t help matters):
The longer answer: It is formed when two proteins found in wheat, barley, and rye (gliadin and glutenin)–are mixed with water. It’s gliadin that causes the immune reaction in celiac disease. Plant scientists call these “storage proteins” because they serve as the protein source for the emerging seedling (remember that these foods are seeds).
Even if you understand what gluten is, and the fact that it’s found in wheat, barley and rye, you may not know all the varieties of wheat that don’t contain the word “wheat” in their name. Here is a longer list of grains that are genetically related to wheat and contain gluten. Remember, many foods contain hidden sources based on these grains:
Wheat (all-purpose flour, bread flour, whole wheat flour, wheat bran, wheat germ, graham flour, pastry flour)
Barley and barley malt
Faro (sometimes spelled farro)
Sprouted wheat, sprouted wheat flour
Yeast brands that contain enzymes or dough enhancers which enhance wheat doughs. Most yeast brands are fine. These enzymes/enhancers are often derived from wheat, so check to be sure your yeast is labeled “gluten free.”