Under the Microscope: Dealing with Diastaticus in the Brewhouse

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.