No, not all tamari is gluten free. While tamari is traditionally brewed with soybeans and no wheat, some commercial brands do include wheat as an ingredient. If you have celiac disease or a gluten sensitivity, you need to check the label on every bottle rather than assuming tamari is safe by default.
Why Tamari Is Usually Wheat-Free
Tamari originated as a byproduct of miso paste production in Japan, and the traditional recipe calls for soybeans, water, salt, and a fermenting mold called koji. No wheat is involved. Soybeans are soaked, cooked, formed into nuggets, and coated with koji. The mixture then ferments in saltwater for four to six months before being pressed and pasteurized into the dark, rich sauce you find on shelves.
This is what separates tamari from regular soy sauce. Standard soy sauce (shoyu) is brewed with roughly equal parts soybeans and wheat, making it off-limits for anyone avoiding gluten. Tamari’s heavier reliance on soybeans gives it a rounder, less sharp flavor and, in its traditional form, keeps wheat out of the picture entirely.
Where Wheat Sneaks In
The problem is that not every manufacturer follows the traditional recipe. Some brands add small amounts of wheat to their tamari, either to adjust the flavor profile or to cut production costs. Kikkoman, one of the most widely available soy sauce brands, produces a tamari that is not gluten free. This catches people off guard because they associate the word “tamari” with “wheat-free” and grab the first bottle they see.
Even tamari made without wheat as a listed ingredient can pick up gluten through cross-contact during manufacturing. If a facility also processes regular soy sauce or other wheat-containing products, shared equipment, storage containers, or production lines can introduce trace amounts of gluten. The Celiac Disease Foundation specifically notes that cross-contact through shared utensils or cooking environments can make otherwise safe foods problematic for people with celiac disease.
What “Gluten Free” on the Label Actually Means
In the United States, the FDA allows a product to carry a “gluten-free” label if it contains less than 20 parts per million (ppm) of gluten. That’s the legal threshold, and for most people with celiac disease, it’s considered a safe level. However, the FDA does not require manufacturers to actually test their products before making that claim. A company can label its tamari “gluten free” based on its ingredient list alone, without running any lab analysis to confirm the final product meets the 20 ppm cutoff.
This gap matters because gluten can enter a product through contamination that wouldn’t show up on an ingredient list. Some manufacturers test every batch rigorously; others may test sporadically or not at all. A study published in the European Journal of Clinical Nutrition found significant variability in how manufacturers verify their gluten-free claims, with some relying on in-house testing methods that aren’t fully validated.
Third-Party Certifications Are Stricter
If you’re highly sensitive, look beyond the FDA label for a third-party certification mark. These programs require actual testing and hold products to tighter standards than the federal rule:
- GFCO (Gluten-Free Certification Organization): Products must test at no higher than 10 ppm of gluten.
- GFCP (Gluten-Free Certification Program): Products must test below 10 ppm.
- CSA (Celiac Support Association): Products must test below 5 ppm, the strictest threshold of the three.
A tamari bottle with one of these logos has been independently verified, which gives you a layer of confidence that the FDA’s self-reported label doesn’t. San-J, for example, brews its tamari with 100% soybeans and no wheat, and its gluten-free varieties carry third-party certification.
Fermentation Does Not Remove Gluten
One common misconception worth addressing: some people assume that the long fermentation process breaks down gluten proteins enough to make wheat-containing soy sauces safe. It doesn’t. While fermentation does break down some proteins, it does not reliably reduce gluten to levels considered safe for people with celiac disease. This applies to both regular soy sauce and any tamari that includes wheat in its recipe. Fermentation is not a workaround.
How to Choose a Safe Tamari
Start by reading the ingredient list. Wheat will be listed if it’s present, and in the U.S. it must also be called out as an allergen. Next, look for a “gluten-free” label, which confirms the product should contain less than 20 ppm. For the highest level of assurance, choose a bottle with a third-party certification seal from GFCO, GFCP, or CSA.
If you’re dining out, don’t assume the tamari at a restaurant is wheat-free. Ask to see the bottle or ask staff whether it’s a certified gluten-free brand. Many restaurants stock whatever soy sauce is cheapest, and a dark sauce labeled “tamari” on the menu may still contain wheat. At home, store your tamari away from wheat-containing condiments and use a clean spoon or pour directly from the bottle to avoid cross-contact in your own kitchen.