Is yeast extract gluten free?

Yeast cells broken open so the savoury compounds inside can be used as a flavouring. That is all the term specifies — it says what was done, not what it was done to. The yeast can be grown deliberately on molasses, or it can be yeast recovered from a brewery after fermenting beer, and both end up on a label as the same two words.

Because the two sources give genuinely different answers and the label does not distinguish them. Yeast extract from molasses-grown yeast is gluten-free. Yeast extract from spent brewer's yeast carries barley protein. The ingredient name is identical in both cases, which makes this one of the small number of entries where reading more carefully cannot help you.

FDA — packaged food

Barley is not a major US food allergen, so there is no obligation to declare it and no obligation to say which yeast was used. The National Celiac Association and the Gluten Intolerance Group both advise avoiding yeast extract in the absence of a gluten-free claim, which is a stronger position than they take on most ambiguous ingredients and reflects how often the brewery route is used.

Elsewhere

The concrete number worth carrying: Marmite, which is a yeast extract product made from brewer's yeast, has tested at around 30 ppm. That is above the 20 ppm threshold at which a food can be called gluten-free, so this is not a theoretical contamination risk — it is a product people eat on toast that would fail the test.

A gluten-free claim on the package resolves it and nothing else does. Without one, yeast extract is worth treating as a no rather than a maybe, which is the advice both US celiac organisations give. It turns up most often in crisps and savoury snacks, stock cubes, gravy, soup, and anything sold as having a savoury or umami flavour.

• National Celiac Association and Gluten Intolerance Group — avoid yeast extract without a gluten-free claim
• 21 CFR 101.91 — 20 ppm limit for a gluten-free claim