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News

The Microbiology of Beer


 

One ancient and potentially overlooked application is microbiology’s relevance to brewing beer. Brewing has been going on for thousands of years and the process has changed drastically over time, especially recently. A recent review compiled hundreds of relevant studies on microbiology’s importance on beer quality from barley field to your glass.

Brewing is a process of fermentation, thus yeast does most of the heavy lifting when producing beer. However, not any yeast will do. Beers can be split into two categories: lagers and ales. Lagers use strains of Saccharomyces pastorianus whereas ales use strains of Saccharomyces cerevisiae. The reason for this is due to the process in which these beers are made. Lagers are fermented at cooler temperatures whereas ales are fermented at warmer temperatures. S. pastorianus is a more complex organism and not isolatable in nature, suggesting that it’s a hybrid of two types of yeast. Studies suggest S. cerevisiae hybridized with S. bayanus to generate S. pastorianus. S. cerevisiae and S. pastorianus both have many strains (S. cerevisiae is much more diverse), which leads to lager breweries keeping their own specific strains of yeast. During the brewing process, some breweries recollect the yeast after fermentation and reuse it to ferment a new batch. Each batch may be slightly different, which may lead to selective pressures favoring a variant in the population, which could lead to a population of yeast that differs from the brewery’s own special strain. In order to combat this, many breweries keep master cultures of their particular strains in order to help reduce the number of variants and maintain a consistent product.

 

Yeast health is also very important. New techniques using light scattering and electromagnetic properties are being used to evaluate yeast health in addition to older methods of staining. Controlling variables like temperature, oxygen levels, and nutrient levels in the wort are also conducive to keeping yeast alive. Alterations in these variables can make products that can have a drastic effect on the beer, usually diminishing its quality.

While yeast may be the star of the show, many other microbes can have an effect on the final product. Fusarium pathogens that grow on barley can produce mycotoxins that inhibit yeast growth or end up in the beer (fortunately, they’re detectable). Lactic acid bacteria help acidify the wort which is favorable for fermentation, but Bacillus strains can cause over acidification and Clostridium can make the beer smell like cheese, just to name a few ways microbe ecology can spoil beer. These consequences can easily be avoided by using proper hygienic techniques.

When the beer is finished, it still has to overcome packaging, transport, and storage. Biofilms may build up in kegs or equipment which could lead to an infected batch. Yet again, proper sterilizing techniques can be used to prevent this. Temperature fluxes and shaking can also damage the final product.

It may seem like there is a bevy of things working against the brewing process.  Luckily for us, beer has science on its side.