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Under the Microscope: Dealing with Diastaticus in the Brewhouse

Determining whether a yeast is a contaminant is like deciding whether a plant in your garden is a weed—it all depends on whether you want it there. The insatiability of diastatic strains can be a danger if uninvited. Properly managed, it can be an asset.

Don Tse Dec 16, 2021 - 10 min read

Under the Microscope: Dealing with Diastaticus in the Brewhouse Primary Image

Photo: Rattiya Thongdumhyu/Shutterstock

A few years ago, diastatic yeast got an eruption of attention that occasionally spilled over into mainstream news; breweries were forced to recall beers and explain why to local drinkers. There was even a high-profile civil lawsuit, with Colorado’s Left Hand Brewing—which had to destroy $2 million in beer—accusing White Labs of selling “contaminated and defective” yeast in 2016. Diastatic yeasts have gained such a negative reputation that many breweries simply play it safe and ban them from the premises.

Of course, there is nothing new about diastatic yeast—they’ve been around and making beer for centuries. However, the proliferation of smaller breweries making a broader variety of beer styles—and often employing a wider range of yeasts—increases the likelihood of the occasional cross-contamination.

What Is Diastaticus?

Saccharomyces cerevisiae var. diastaticus are strains of ale yeast with a special ability: They secrete an enzyme called glucoamylase, which breaks down otherwise unfermentable dextrins into simple sugars. The yeast can then ferment these simple sugars, leading to a beer that is drier, stronger, and more highly attenuated.

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Don Tse is an internationally recognized beer writer and beer judge, working from his home base in the middle of North America’s barley belt.