Diastaticus Days: Part 1 – where to start…

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So myself (Josh) and Fabio have been a bit poor in attending to our blog, we hope to rectify this in the future!

And guess what this post is on?!


I’m going to split this post into two, one (this one) on what it is and what it does. And then a second on why we are organising Diastaticus Days and what we hope to provide and achieve!

It probably looks like we’re a bit obsessed by this topic. I won’t lie, it has taken over a lot of our waking hours in recent weeks, but I think it’s worth it.

So for those who are unaware (i.e. not beer nerds like us), there is a variant of brewing Saccharomyces cerevisiae floating around out there in the wild and in some culture collections (~40 strains at last count) that goes by the sub-name of diastaticus. These strains are slightly unique in the brewing yeast world, in that they, in contrast to your standard cerevisiae, possesses a single gene (STA1) encoding a protein that is causing a whole lot of fuss. This protein is an extracellular glucoamylase (also known as amyloglucosidase), an enzyme that can cleave off the glucose molecules from the ends of long chains of sugars releasing it into solution.

Why it this bad you might think?

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What's in a name?

Saccharomyces cerevisiae var. diastaticus

Having the property to breakdown long-chain sugars such as starch to simple sugars like glucose is referred to as being diastatic. Diastatic power is a term typically used when referring to grains, and the ability of their enzymes to break down starch to glucose. So in this case we can describe diastaticus as potentially being diastatic.

I also think it makes it sound dangerous and a bit evil, but thats just me. I actually really like these yeast… WYeast 3711 French saisons is one of my favourites!

Say you’re making your favourite tasty Belgium Pale Ale (not too dry and not too strong ABV wise), and you’re either using a diastatic strain or have angered the brewing pantheon and suffered a contamination. Normally once fermentation has ceased (fermentable sugars have been consumed and gravity is stable, etc.), you would go ahead and cold-crash it and process it via your packaging method of choice. Well, it might be that having done so, the diastatic yeast could pull a fast one on you and begin excreting its glucoamylase into your lovely Belgo pale ale. This is where problems might begin.

The glucose released by the diastaticus glucoamylase and other fermentable sugars could effectively restart fermentation in your packaged brew. All the yeast in that bottle (be they diastatic or not) then have the potential to metabolise those sugars, producing more ethanol and carbon dioxide. That pale ale could easily become a double pale ale with a serious case of ‘gushing’ and ‘bottle bombs’ syndrome. But in seriousness, this does happen and it does result in batches being dumped and packaged products being recalled. If you have stated your beer is 3.5% ABV, but it is now 4.5% due to re-fermentation, this can cause issues with the authorities, especially in my own beloved Sweden where there are different regulations for different strengths of beer.

Even when you know you are using a diastatic strain, like in the case of saison yeast, which are pretty much all STA1 positive - check out our list), it is still tricky to get the final product out to the consumers how you want it to be. Should the yeast suddenly decide to start making said enzyme, one batch might not behave the same as another should something make the yeast start producing its diastatic enzymatic payload.

And therein lies another problem, very little is known about how the production of this enzyme is regulated by the yeast. What environmental conditions switch on production and excretion of the glucoamylase? Temperature, pressure, a low carb diet?  To complicate matters, a significant number of strains with STA1 gene present in their genome don’t even appear to show this diastatic ability! They are not functionally diastatic. This hasn’t stopped suppliers listing all of the strains that are STA1+ in their collections though, which is probably out of caution given recent judicial proceedings. We wonder if this status will put people off using some yeast due to the possible worry of these issues, but time will tell.

There are already some great studies starting to come out on these strains, mainly from the exceptional Weihenstephan Research Centre for Brewing and Food Quality (links below). These are likely to become seminal works in the field as it develops. Even brewing association such as the Masters Brewers Association of the Americas (MBAA) have addressed concerns about this in the industry by recently running a very handy seminar.

A great paper! And its open access. Read it!

A great paper! And its open access. Read it!

But for now, ourselves and a number of other enthusiastic beer and yeast scientists around the world are attempting to unravel this problem by screening all of the strains we can get our hands on, be they in collections or isolated from breweries.

In fact, we even have a MSc project available on this subject at the moment!

In the next post, I will explain what has specifically led us to run a special program on the detection and identification of diastaticus, as well as how we hope this information and projects could help the industry.

Any questions or comments, just drop them below and I’ll try and answer or calmly argue with you :-)