Scientists may have found a way to inhibit unwelcome strains of yeast from over-fermenting craft brews
When diastatic strains of Saccharomyces Cerevisiae, or brewer’s yeast, contaminate the brewing process, it can become a major problem for craft beer brewers. Diastatic yeasts are strains of yeasts that secrete glucoamylase, an enzyme that breaks down dextrins into simple sugars. These can spoil fresh beer production by augmenting the alcohol content, changing the flavour and, in worst-case scenarios, making bottles of beer explode.
According to a scientific article published in Applied and Environmental Microbiology on 12 September, a group of brewers and microbiologists found that proteins called killer toxins, which are produced naturally by many strains of brewer’s yeast, can suppress the impact of diastatic strains. “If you’ve got a diastatic contamination, most of the time you just throw away the beer, and that’s expensive,” said microbiologist and senior author Paul Rowley, Ph.D., at the University of Idaho. “What we show in the paper is that we can add the killer yeast at the point of contamination. It’s a remediation procedure to prevent the diastatic strains from taking off.”
Although diastatic strains of yeast play an important role in brewing Belgian-style saison beers, which often have a higher alcohol content than other styles, those strains can end up in the mix of other types of beer and set off a secondary fermentation. Although many breweries do have surveillance methods to try and prevent contamination, the strains can slip by.
Larger breweries often avoid the problem by pasteurising beer, but the process is expensive, and some small brewers believe that pasteurisation changes the taste, according to Nicholas Ketchum, a microbiologist who works at the Rhinegeist brewery in Cincinnati, Ohio, and is a co-author on the study.
Over several years of study, the researchers subjected 34 diastatic strains of yeast to Saccharomyces strains producing eight known killer toxins. They discovered that the most effective toxin, K1, prevented the growth of more than 91% of the diastatic strains tested. The next step will be to better understand the mechanisms of the process, said Ketchum, and to find a way to make it useful to craft brewers.
