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. So today, let’s take a look at the role of lactic acid bacteria in beer!

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.

The Impact of Lactic Acid Bacteria in Beer

Lactic acid bacteria play a pivotal role in shaping the flavor profile of sour beers, which have gained popularity in modern craft breweries. Understanding the nuances between Lactobacillus and Pediococcus is crucial for brewers aiming to craft complex and balanced sour ales. Lactobacillus, akin to its presence in yogurt, swiftly acidifies beer within hours, delivering the desired pH without compromising taste. However, its sensitivity to hops and rapid pH changes necessitate careful monitoring during fermentation.

Contrastingly, Pediococcus operates on a slower timeline, requiring months to manifest a noticeable pH drop in beer. This deliberate pace aligns with the production of aged beers like lambics, granting ample time for yeast activity before acidity intensifies. Yet, the extended aging process carries risks, such as the development of undesirable flavors like diacetyl. Brewers must exercise patience and precision to mitigate these challenges while nurturing the beer’s maturation.

While lactic acid bacteria remain fundamental to beer acidity, emerging yeast strains, such as those from the Lachancea genus, introduce intriguing possibilities. The prospect of yeast capable of concurrently producing lactic acid and alcohol showcases the dynamic nature of brewing science. As experimentation continues, brewers are poised to explore innovative avenues for crafting distinctive and memorable brews that challenge traditional conventions.

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.

More Sources on Acid Bacteria in Beer

1. Tonsmeire, M., American Sour Beer: Innovative Techniques for Mixed Fermentations, Brewers publications, Boulder, Colorado, United States, 2014.
2. New Product Announcement: WildBrew™ Philly Sour, L’Allemand
3. Brewing With Lactobacillus, Brew Your Own
4. pediococcus, Beer and Brewing
5. LSB7003 – PEDIOCOCCUS, LeLabo Solutions Brassicoles
6. The Microbiology of Malting and Brewing by Graham G. Stewart on Journal of the Institute of Brewing – Wiley Online Library
7. Sour Beer: Research and Development by Michael Tonsmeire on American Homebrewers Association – American Homebrewers Association
8. Brewing Microbiology: Managing Microbes, Ensuring Quality and Valorising Waste by Alexandre da Silva Duarte and Patricia Alexandra da Silva Lopes on Frontiers in Microbiology – Frontiers
9. Lactic Acid Bacteria: From Starter Cultures to Probiotics by Maria Saarela, Johanna Mättö, Raija-Liisa Heilig, Jarmo Harmsen, and Seppo Salminen on SpringerLink – SpringerLink
10. Sour Beer Production: A Review of Current Knowledge and Methods of Production by Justin A. Miller, Jeffrey M. Manderfeld, and Christopher J. Fields on Comprehensive Reviews in Food Science and Food Safety – Wiley Online Library
11. Lactic Acid Bacteria in Traditional Foods by L. Axelsson on Food Science and Technology – ScienceDirect
12. Brewing Microbiology: Current Research, Omics Technologies and Future Trends by Laura Steen, Jonas Almeida, and Willem M. de Vos on Microbial Biotechnology – Wiley Online Library
13. Microbiology of Belgian Sour Beer Production by Luc De Vuyst and Frédéric Leroy on the National Library of Medicine – PubMed
14. Lactic Acid Bacteria and Their Metabolic Products for the Control of Fungal Infections in Human Beings: A Review by F. U. Ajabnoor on Journal of Applied Microbiology – Wiley Online Library
15. Advances in the Microbiology of Fermented Foods and Beverages by Charles W. Bamforth on Annual Review of Food Science and Technology – Annual Reviews