Brewer's Yeast Amino Acid Profile: Lysine, Methionine and How to Use the Numbers

In short: dried brewer's yeast carries lysine at about 6.3% of its protein, level with soybean meal, and glutamic acid at about 14.7%, the amino acid behind its savoury taste. Methionine sits near 1.5% of protein, so formulators balance it from other ingredients. TBESBY specifies lysine at 30.5 g/kg of product. The table below gives the full profile from Feedipedia.

This page is written for nutritionists and formulators in pet food, aquafeed and livestock feed who need amino acid figures for a matrix value, and for buyers who want to know which numbers to request from a supplier.

What is the amino acid profile of brewer's yeast?

The figures below are literature averages for dehydrated brewer's yeast, expressed as a percentage of crude protein. They come from the Feedipedia datasheet compiled by INRAE, CIRAD, AFZ and FAO. Use them as a starting matrix and replace them with the supplier's own analysis once you have it.

How does it compare with fish meal and soybean meal?

Per unit of protein, brewer's yeast matches soybean meal on lysine and methionine and sits below fish meal on both. That is why it works as a partial replacement for either, with the methionine balance closed elsewhere in the recipe. The wider comparison, including fibre and DDGS, is in our nutrient profile guide. Source for all three rows: Feedipedia.

How do formulators use these numbers?

• Convert to an as-fed basis. Multiply the percentage of protein by the crude protein on the certificate of analysis. At 43% protein, threonine at 4.4% of protein is about 19 g/kg of product.
• Count the contribution at the real inclusion rate. At 2% inclusion and 30.5 g/kg lysine, brewer's yeast adds 0.61 g of lysine per kg of diet.
• Apply species digestibility. Total amino acids are the starting point; use the digestibility coefficients your formulation system holds for the target species.
• Read glutamic acid as a palatability figure as well as a nutrient. It is one reason brewer's yeast is used in dog and cat food at 1 to 3%.

Why do published values vary?

The Feedipedia average for crude protein rests on 108 analyses and runs from 39.3 to 56.8% of dry matter. Amino acid averages rest on far fewer samples, four to eight for most of them, so they describe the ingredient in general and no single product. Yeast strain, brewing recipe and handling before drying all move the figures, which is why reviews such as Jaeger and colleagues (2020) report protein as a range. A drum-dried product from one producer, made from yeast collected at the same breweries month after month, varies much less than the literature range suggests. That is the reason to ask for the supplier's own analysis and to keep your matrix values tied to it.

What do the percentages mean in grams per kilogram?

Formulation software works in grams per kilogram of product. The table below converts the literature percentages across the TBESBY protein specification of 40 to 46%. The values are calculated and indicative. Lysine is the exception: 30.5 g/kg is the TBESBY specification value.

What does the research say about using it as a protein source?

Feedipedia summarises the pig literature in one line: brewer's yeast contains most essential amino acids in adequate quantities for pigs, with methionine and cystine the pair to balance from other ingredients (Huige, 2006). Blair (2007) recommends 2 to 5% of the diet for pigs, and the same range is usual in poultry. For poultry the datasheet describes it as a protein of high biological value and digestibility, and Ergül (1988) replaced fish meal with dried yeast at up to 9.3% of broiler diets.

In companion animals the best controlled data come from Davenport and colleagues (2023) in Translational Animal Science. They fed extruded dog and cat diets with dried yeast at 10%, in place of pork meal and wheat middlings, and found nutrient digestibility and stool quality unchanged in both species, with a preference for the yeast diet in two-bowl tests. Ten percent is three to ten times the commercial rate of 1 to 3%, so the amino acids in the table above are being delivered in a form the animals digest. Our palatability guide covers that trial in detail.

How do you balance the sulphur amino acids?

Methionine and cystine together come to about 2.4% of yeast protein in the Feedipedia table. Soybean meal sits at a similar level and fish meal higher, so a formula that swaps part of its fish meal for yeast usually tops up methionine with a synthetic source or with another protein that carries more of it. At the 1 to 3% used in pet food the adjustment is small. At the 5 to 10% used in some aquafeed and piglet formulas it is a line the formulator checks in the matrix, and it is a routine one.

What should you ask a supplier for?

Ask for crude protein and lysine on the specification, the laboratory method, and an amino acid analysis from an accredited laboratory for matrix work. TBESBY provides these with the Brewer's Yeast Formulation Kit, together with a sample for your own analysis.

Source: Feedipedia, Brewers yeast datasheet (INRAE, CIRAD, AFZ and FAO), feedipedia.org/node/72.

Further sources

• Jaeger, A., Arendt, E.K., Zannini, E. and Sahin, A.W. (2020). Brewer's spent yeast (BSY), an underutilized brewing by-product. Fermentation, 6(4), 123.
• Davenport et al. (2023). Translational Animal Science: dried yeast in extruded dog and cat diets.
• Blair (2007), Huige (2006) and Ergül (1988), as cited in the Feedipedia datasheet.