Sour Beer Q&A With the Lallemand Brewing Technical Team

With every new product, we inevitably get many questions about how the strain works and how to optimize its performance. This is especially true for our sour strains from the WildBrew^® Series and the Sourvisiae^®* from Mascoma. We love hearing your questions and feedback! Here are some of the most common questions we receive about making sour beer.

How does lactic acid affect density, attenuation, and ABV?

Lactic acid is about 20% more dense than water. Despite this fact, you can still use a standard ABV calculator based on densities to determine the alcohol level of a sour beer. This is because CO2 is only lost when alcohol is formed during fermentation by the yeast, and not during the formation of lactic acid.

Therefore, any change in density is related to alcohol formation. This is why you don’t see a density drop during your kettle sour, even though sugars are consumed by the bacteria. Attenuation calculations, on the other hand, can be misleading in the context of a sour beer. Real attenuation is the percent of sugar that is consumed during fermentation. For sour beers, lactic acid contributes to a higher final gravity (and lower attenuation) compared to a regular beer fermentation consuming the same amount of sugar (real attenuation is the same).

How acid tolerant is my yeast strain?

While high concentrations of organic acids stress the fermenting yeast, the good news is that most yeast strains are quite tolerant to acid levels normally found in sour wort (<0.4% lactic acid). Above this level, some strains start to lose their ability to metabolize maltotriose to varying degrees resulting in slower fermentation and lower attenuation. Our internal research confirms that dry yeast is perfectly suitable
for dry pitching directly into sour wort without any problems.

For very sour beers, yeast strain selection is important. We recently published a characterization of some of our LalBrew^® Premium Series yeast strains for fermentation performance in the presence of lactic or acetic acids.₁

Why are yeast for sour beer production such as Sourvisiae^®* and WildBrew PhillySour™ not repitchable?

Some have asked us if Sourvisiae^®* was selected specifically to be non-repitchable as part of the genetic engineering process. The answer is no – the high acid environment at the end of fermentation reduces the viability of the yeast making it unsuitable for repitching, similar to the behavior of most Saccharomyces cerevisiae strains. For WildBrew Philly Sour™, lactic acid is produced from simple sugars at the start of fermentation before switching metabolism to fermenting other sugars into ethanol. When repitching WildBrew Philly Sour™, the yeast may not switch back to lactic acid metabolism resulting in little to no lactic acid in the second generation.

How do I select the best strain(s) to brew specific sour styles?

Lactic acid bacteria and yeast will vary in their flavor and lactic acid production. The same flavor considerations apply when selecting a yeast strain to ferment a kettle soured wort: esters, phenolics, and attenuation. We have a unique tool on our mobile app that will recommend a combination of bacteria and yeast, a pure lactic acid yeast, or a blend of lactic acid yeast and regular brewing yeast to achieve your desired flavor and performance. Check out the LalBrew App to try it for yourself!

1 Shayevitz, A., Abbott, E., Van Zandycke, S., & Fischborn, T. (2021). The Impact of Lactic and Acetic Acid on Primary Beer Fermentation Performance and Secondary Re-Fermentation during Bottle-Conditioning with Active Dry Yeast. Journal of the American Society of Brewing Chemists. 80. 1-12.
* Sourvisiae^® is a bio-engineered yeast only available in the US