Story Time: Diastatic Fake Outs

In scary stories of expensive lessons with diastatic yeast, things like exploding packaging take most of the limelight. But there are other tales, trickier ones you might not have heard of. Here are two that highlight some important things to know about detection methods for diastatic contamination.

Non-living diastatic yeast matter

A brewery had a positive hit for diastaticus in one of their beers using PCR-based detection. They audited their process starting from their yeast pitch, which they had tested before use (a great best-practice) and confirmed it was negative for diastaticus. After a first-stage propagation, still negative. After pitching into their hazy IPA, disaster: positive.

They’d seen this pattern over multiple separate pitches. And they’d destroyed a good portion of beer based on the results. In pursuing the source of the contamination, and after a lot of investigation, it turned out the trigger for the hit was a haze-helping additive which just happened to contain yeast matter from dead diastatic yeast cells. That meant the STA1 DNA was indeed present as the test was alerting to, but it wasn’t actually a threat for over attenuation and off flavors. That meant they had dumped beer needlessly.

How could this have been prevented? If they had been doing plating alongside PCR testing, for example, it’s likely they would have pursued answers to why diastaticus was detected by PCR but was not growing on selective media. They might have discovered sooner that it was a kind of false positive. This is a great illustration for why it’s effective to use multiple methods of detection.

Non-conforming copper resistance in a non-diastatic strain

A brewery was using an outside lab for diastatic testing. The brewery had not opted for DNA-related testing, only plating. Results were coming back from the lab as positive for diastatic yeast on LCSM. The lab was reporting that to the brewery as confirmation of the presence of diastatic yeast.

At the brewery’s request, Omega Yeast’s lab services later verified their LCSM results. Omega Yeast always uses DNA-based testing after detecting a positive LCSM hit because of the possibility of false positives. When results were checked via DNA-based methods, it was revealed that the LCSM hit was a false positive. The brewery had been using a kveik strain. Kveik is not diastatic. But, perhaps because of its unique origin relative to our other brewing strains, copper sensitivity hasn’t tagged along in the same way. So, testing via copper sensitivity/resistance wasn’t helpful in identifying it.

Remember that copper resistance is a correlated trait in most of our diastatic strains, that’s why we use it as a detection method, but it’s not really connected to diastatic activity. There are exceptional strains that do not conform.

This goes to show that even labs could benefit from understanding diastatic strains better — and the tests that detect them; LCSM is a great resource, but you can’t answer all of your questions with it.

In response to scares like these, and a general penchant for leaving things better than they found them, Omega Yeast’s researchers looked into developing new tests to add to the mix, ones that aren’t prone to any false positives like these (or false negatives for that matter). These new tests look for diastatic yeast by diastatic activity directly, rather than by copper resistance. As an ancilliary benefit, they can also tell you how strongly diastatic a contaminating strain is. Knowledge is power with diastaticus. Additional detail always comes in handy.