Brewer’s Yeast in Cat Food: Palatability, Protein and Use Levels

Brewers dried yeast is used in cat food for three reasons: cats like the taste, it adds digestible protein, and it is a natural source of B-vitamins. In a 2023 feeding study, cats offered a kibble with 10% dried yeast ate about twice as much of it over two days as the same kibble without yeast, with no change in digestibility or stool quality. Commercial cat formulas use far lower levels, typically a few percent, mainly for palatability.

This guide covers what the ingredient is, what the evidence shows in cats, how it appears on a label, and what to check before you add it to a formula.

What is brewers dried yeast?

Brewers dried yeast is Saccharomyces cerevisiae recovered after beer fermentation, inactivated and dried into a light brown powder. The yeast is no longer alive, so it does not ferment or grow in the food. In feed it supplies protein, free amino acids and nucleotides that give a savoury taste, B-vitamins, and cell-wall components such as β-glucans and mannans.

It is a co-product of brewing, not an alcohol ingredient: the yeast is separated from the beer and dried. Pet owners sometimes search for “alcohol by-products in cat food”; on a label, brewers dried yeast refers to the dried yeast cells.

Why do cat food makers use it?

• Palatability. Cats are selective eaters, and acceptance is often the first test a new formula has to pass. Yeast’s free amino acids and nucleotides add an umami note cats respond to.
• Protein. Dried brewer’s yeast carries 40–46% crude protein and is well digested, so it contributes to protein targets without adding fat.
• B-vitamins. Yeast is naturally rich in B-vitamins, including thiamine, which cats need in their diet.
• Clean-label fit. It is a single, recognisable ingredient with an established feed definition, which suits natural and limited-ingredient positioning.

What does the research show in cats?

The most direct evidence comes from a 2023 study in Translational Animal Science that tested dried S. cerevisiae at 10% of an extruded diet against the same diet without yeast, in both cats and dogs.

Two points matter when reading this. It is a single study, and 10% is well above typical commercial use. What it shows is that cats clearly prefer a yeast-containing kibble and that yeast at that level did not upset digestion. Your own palatability test on your own base formula is still the deciding step.

How much is used in cat food?

Commercial dry cat and dog foods typically include brewers dried yeast at around 1–3% of the recipe, where it works mainly as a palatant and B-vitamin source. Higher levels have been tested in research, as above, but there is little published data on long-term feeding of high levels to cats. Start low, test acceptance, and adjust.

How does it appear on the label?

• United States: “brewers dried yeast”, the AAFCO ingredient name (definition 96.4), which sets a minimum of 35% crude protein.
• European Union: brewers’ yeast is listed in the Catalogue of Feed Materials, Regulation (EU) No 68/2013, entry 12.1.5.

See our guide to brewer’s yeast in feed regulations for the full definitions.

What to check before adding it to a cat formula

1. Ask for the analysis. Crude protein, moisture and ash on a recent Certificate of Analysis. Our guide on how to read a brewer’s yeast CoA explains each line.
2. Confirm it is brewer’s yeast. Molasses-grown or ethanol yeast is a different ingredient with a different label name.
3. Check bitterness. Spent brewer’s yeast can carry hop residues. Ask whether the product is suitable for pet food, or consider a debittered brewer’s yeast.
4. Run an acceptance test. A two-bowl test against your current formula tells you more than any spec sheet.
5. Plan the supply. Agree packing (25 kg bags or 600–1,200 kg jumbo bags), shelf life and storage so the ingredient stays dry and free-flowing.

Sources

• Davenport GM, Block SS, Adolphe JL (2023). Translational Animal Science 7: txad107
• AAFCO. Ingredient definitions, section 96 (Yeast)
• Commission Regulation (EU) No 68/2013 on the Catalogue of feed materials
• Feedipedia. Brewers yeast