Rennet is gluten free. Whether you’re using animal, vegetable, microbial, or fermentation-produced rennet, the active ingredients are enzymes derived from animal stomachs, plants, or fungi, none of which contain wheat, barley, or rye proteins. This applies to liquid, tablet, and powder forms alike.
Why Rennet Is Naturally Gluten Free
Rennet’s job is to coagulate milk into curds during cheesemaking, and its key components are proteins (enzymes), not grain-based ingredients. Traditional calf rennet is roughly 90% chymosin and 10% pepsin, both enzymes extracted from the stomach lining of young calves. Vegetable rennet comes from plants like the cardoon thistle, which produces its own coagulating enzymes called cyprosin and cardosin. Microbial rennet is made by fungi such as Rhizomucor species, which generate proteases that mimic calf chymosin. Fermentation-produced chymosin (FPC) takes the calf gene responsible for chymosin and inserts it into a microorganism that then produces pure chymosin.
None of these sources involve wheat, barley, rye, or any other gluten-containing grain as a functional ingredient.
Where Cross-Contamination Could Theoretically Occur
The enzymes in microbial and fermentation-produced rennet are grown on nutrient media in controlled fermentation tanks. While these growth media can vary by manufacturer, they typically use sugars, salts, and nitrogen sources rather than grain-based substrates. The final enzyme product is purified and separated from the growth medium before sale. Still, if you have celiac disease and want absolute certainty, checking with the specific manufacturer is the most reliable step, since cultivation media details aren’t always disclosed on the label.
Tablet forms of rennet sometimes contain fillers or binders to hold their shape, which is another spot where gluten could theoretically appear. In practice, major cheesemaking suppliers explicitly label their rennet tablets as gluten free. New England Cheesemaking Supply Company, one of the largest U.S. retailers, confirms that all of its rennet products, including liquid chymosin rennet, liquid vegetable rennet, and vegetable rennet tablets, are free from wheat and gluten.
What About the Cheese Itself?
Rennet is only one ingredient in cheese. Most plain, natural cheeses (cheddar, Swiss, Parmesan, mozzarella) are gluten free because their ingredients are simply milk, cultures, salt, and enzymes. The gluten risk with cheese comes from other places: flavored or seasoned varieties that add ingredients like beer, breadcrumbs, or malt vinegar; processed cheese products that may use modified food starch derived from wheat; and cross-contact during slicing or packaging on shared equipment.
If you’re making cheese at home and following a gluten-free diet, the rennet you purchase is very unlikely to be a problem. Your bigger concerns are the other additions, like any herbs, spices, or washes you apply during aging.
How to Verify a Specific Product
Look for “gluten free” on the rennet packaging or product listing. Many suppliers now include full allergen statements covering the top allergens including wheat. If no allergen statement is available, contact the manufacturer directly and ask two things: whether the product contains any wheat-derived ingredients, and whether it’s produced in a facility that also handles wheat. For fermentation-produced or microbial rennet, you can also ask what the fermentation substrate is, though most manufacturers consider this proprietary.
In the U.S., any food labeled “gluten free” must contain fewer than 20 parts per million of gluten. This threshold is considered safe for people with celiac disease. If a rennet product carries this label, it meets that standard.