Foreword: Jocelyn Bernier-Lachance is a home brewer with some ten years’ experience. He is also a microbiologist by training, having previously worked for the Lallemand company, the Gallicus craft brewery and La Chope à Malt/Beer Grains. Today, he’s eager to share his experience with you and spread his passion for microorganisms and fermentation.
Fine weather is just around the corner! This is the time of year when breweries start offering us sour beers. We’ve all tried a fruit beer sour enough to pickle our tongues, but how do brewers do it? With the help of lactic acid bacteria.
There are two main types of lactic acid bacteria used to make beer: Lactobacillus and Pediococcus. Unlike yeast, these bacteria produce lactic acid during fermentation.
In the sour beers commonly found in modern breweries, Lactobacillus is the most widely used. These bacteria are also found in yogurt. In just a few hours, they can acidify beer to the desired pH without altering its taste. They work fastest at temperatures of around 40 degrees Celsius. However, they are sometimes too fast for yeasts, which can suffer from such rapid pH changes. What’s more, they are not very tolerant of the presence of hops.
A level of hops above 8 IBU is sufficient to inhibit the growth of most commercial strains. This is why the use of a massive quantity of overaged hops (aged and therefore less rich in IBU) in traditional Belgian sour beers allows the pH drop to be slowed down long enough for the yeast to do its job properly.
Pediococcus, on the other hand, takes months to cause a noticeable pH drop in a beer. This is why they are used in the production of aged beers such as lambics and other traditional Belgian sour beers. This gives the yeasts plenty of time to finish their work before the pH drops. However, if the beer is not allowed to age long enough, a popcorn taste (caused by the presence of diacetyl) will appear. Unlike yeasts, Pediococcus cannot degrade the diacetyl they produce. If yeast is added to the beer, it will take care of this instead.
Although lactic acid bacteria are still the main way to acidify beer today, a new kind of yeast may well compete with them. Belonging to the genus Lachancea (no, but what a beautiful name!), this yeast produces both lactic acid and alcohol.
For more advice, consult our friends at BeerGrains in Gatineau.
Sources
- Tonsmeire, M., American Sour Beer: Innovative Techniques for Mixed Fermentations,
Brewers publications, Boulder, Colorado, United States, 2014.
- https://www.lallemandbrewing.com/en/australia-new-zealand/blog/wildbrew-philly-
sour-explore-the-yeast-biodiversity-universe/ , consulté en ligne 2023-06-16. - https://byo.com/article/brewing-with-lactobacillus/ , consulté en ligne 2023-06-20.
- https://beerandbrewing.com/dictionary/fwiGJBqg32/ , consulté en ligne 2023-06-20.
- https://lelaboyeast.com/products/lsb7003 , consulté en ligne 2023-06-20.
