From Nestle’s website
Gluten is a protein found in grains including wheat, oats, barley, and rye. Itâ€™s also very commonly used in packaged foods to prevent crumbling. So in addition to the obvious sources like breads, pizza crust or pasta, youâ€™ll find gluten in other unlikely things like licorice, soy sauce, malt vinegar, as well as many flavourings, processed foods, self-basting turkeys, cold cuts, prepared stocks and soups.
Gluten is also the binder in some pharmaceutical products, and it can be the starch listed as â€œunidentified food starchâ€, â€œmodified food starchâ€, â€œcaramel colourâ€, and â€œhydrolyzed plant or vegetable proteinâ€. And when a label simply lists â€œnatural flavoursâ€, â€œflavour extractsâ€ or â€œspice extractsâ€, be careful â€“ gluten may be used in processing them.