Project Results

Beer brewers can use malted barley as a source of naturally-occurring bacteria in the production of sour wort.  This experiment is designed to assess the variation of bacteria found in malted barley across variables including harvest year, varietal, origin, and processing.  The results show there is much in common between bacteria found in malted barley and resulting organic acid and alcohol production regardless of variables. 

About This Project

Sour beers are likely the original beer style and have made a recent comeback in terms of popularity among craft beer enthusiasts. They are made with a bacterial and fungal mix rather than pure cultures of Saccharomyces. yeast as in typical ales and lagers. However, the suite of different microbes and their relative abundances during the course of souring and fermentation remain a mystery. We aim to map part of the sour beer microbiome and identify the organic acids these microbes produce.

Ask the Scientists

What is the context of this research?

Sour beers are delicious, refreshing, and a microbiological mystery. A typical ale is made by using yeast to convert sugar from malted barley (wort) into alcohol and carbon dioxide. During sour wort production, naturally occurring bacteria and wild yeast found on malted grain can be used as an affordable way to inoculate and sour wort. With temperature control, one can promote strains of bacteria in the wort to produce lactic acid while limiting the amount of undesirable flavor compounds. Although some have investigated the microbes present in Belgian-style spontaneously fermented beer, the microbial community found on grain and how it changes during the production of sour wort (the sour beer microbiome) is largely unknown.

What is the significance of this project?

Sour beers are a trending category among American craft beer drinkers, but making them is more of an art than a science because we simply don't know enough about the process. When a batch fails for any reason (e.g., poor souring, undesirable byproducts, poor fermentation, or poor carbonation), it's a waste of time and money for the brewers, resulting in higher prices for beer drinkers. If we can understand souring at the microbial level, we can tame it, yielding predictable batches of beer time and again. Additionally, the affordability of utilizing naturally occurring bacteria found on grain (sour-mashing or sour-wort), if controllable, will yield an easy, accessible way for all brewers to experiment more with sour beers.

What are the goals of the project?

The object of this experiment is to determine the microflora on various malted grains and to sample souring beer at various time points to determine which microbes thrive, grow, and ferment during wort-souring. Blue Owl Brewing will collect the samples over the course of 24 h. The Bochman lab at Indiana University will then isolate microbial DNA and prepare next-generation sequencing libraries. The DNAs will be sequenced and the samples compared to one another to: 1) determine the species present and their relative abundances at each time point; and 2) how that microbial community changes with time. The organic acids in the final beer (lactic acid, acetic acid, etc.) will also be identified, as these are the compounds that the tongue recognizes as "sour".