Is ketchup gluten free?

What the sources tell us

The Gluten Intolerance Group puts specialty ketchup in its group of items that are usually gluten-free but could potentially contain gluten. It says some brands may use additional ingredients like malt vinegar or miso, which may not be gluten-free.[2]

Malt vinegar is the clearest case. The group says malt vinegar is fermented and made from barley, and NIDDK lists malt vinegar among the forms in which barley may be found.[2][1]

Vinegar in general is a different story. The National Celiac Association explains that 100% distilled vinegars are gluten free, because gluten proteins are heavy molecules that cannot vaporize and stay behind during distillation. Malt vinegar is the exception it names: it is typically not gluten free in the US because malted barley flavoring is added after distillation.[4]

For that reason the association recommends reading the ingredient list on vinegars, especially specialty or flavored ones, to make sure no gluten-containing ingredients have been added.[4]

Miso, the other ingredient the group mentions, is made by fermenting soybeans with salt and koji, which are cultured grains such as barley or rice. The group says versions made with barley must be avoided.[3]

The same hidden gluten article explains that labels must name wheat, but there are no required warnings for barley or rye, because the FDA does not consider those grains major allergens. It says people who are sensitive to gluten from wheat, barley and rye must be more diligent about reading food labels.[2]