I’m little confused by the AA quoted by yeast labs for STA+ (var. diastaticus) strains. WLP565 is a diastaticus strain, but White Labs quotes it as only 78-80% AA. Imperial’s Rustic is also a diastaticus strain, and they quote a modest 72-76% AA.
Per the MBAA, “Saccharomyces cerevisiae variety diastaticus (S. cer. var. diastaticus) is a type of yeast that can cause unwanted superattenuation…” But I would hardly consider 76% AA “unwanted superattenuation”.
What am I missing?
Well, either Imperial’s Rustic is not a true STA+ strain or they are being conservative. With most strains, AA is just a guideline because mashing regime has a say in wort composition, but with STA+ strains mash temperature has less bearing on final AA because these strain produce diastase, which can hydrolyze starch and dextrin to maltose.
Small correction if I may:
Produces glucoamylase
Hydrolyzes dextrins into glucose
+1
Most likely, the AA percentages for many of these strains are incorrect, still not fixed from before the time when they learned that the strain was diastaticus.
Also possible, the strain might test genomically as diastaticus, but does not actually express the gene for some reason. Kind of like, I had my DNA tested and I am supposed to have blue eyes, but I have hazel eyes. shrug It happens.
I’ve wondered about this with some kveik strains.
Hypothesis #1: Yeast companies don’t run a ton of tests, or personal preference/comfort level plays a big part.
You see different companies list different fermentation temperature ranges and attenuation ranges. My (completely unsupported hypothesis) is that older strains have consistent specs because they come from a more commercial environment. Newer strains and more companies test at different temperatures, and have different comfort levels for risk. I mention a kveik strain, but these are roughly the same yeast strain these different companies provide and depending on what expert you listen to, you can ferment from 65-110 F and have a good ferment of 70-85% attenuation.
Loki (Voss)-65-100F, 75-85% AA
Omega Voss-72-98F, 75-82% AA
Yeast Bay Voss-70-100F, 78-83% AA
Escarpment Voss-77-108F, 70-75% AA
Lars Garshol Registry-43C (109.4F) Max, 80%
Lalbrew Voss-95-104F (Traditional brew), 77-104F, medium-high attenuation
You have to consider that companies can’t afford to test whether a strain works at 68F vs. 70F, or 95F vs 100F. Or the person at Lalbrew might have a better tasting panel or testing capability.
Hypothesis #2: Yeast is weird and cool.
On the other hand, if you look at Omega yeast, a STA1 positive strain can have an AA% of 82-90% (OYL200 Tropical IPA), 74-79% (OYL042 Belgian Saison II), and 78-88% (OYL210 Brett Blend 1). You can make opioids with yeast. Isaac Asimov writes about a yeast factory in “Caves of Steel”, where yeast is use to make artificial strawberry product. Omega talks up strawberry/pear/stonefruit flavors in their CRISPR Sundew strain. Yeast is weird and cool, and we only pretend to understand it.
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I do wonder if this might be at play. Most of the companies say something like “This strain tested positive for the STA gene by PCR analysis.” Didn’t White Labs get sued by a brewery over possible diastaticus contamination? I think they won in the end, but that would give the labs a strong incentive to loudly announce any strain that might exhibit diastaticus behavior – irrespective of how strongly the gene is expressed.
Both of these seem plausible.
Brewing software is a simplified mathematical model of a ridiculously complicated biological process. But my MS is in, basically, applied mathematical modeling; so I like to know where the numbers feeding into the model are coming from and what the caveats are. Garbage in, garbage out, etc, etc.
As does recipe
Indeed, the main value of attenuation ranges from a manufacturer are to get an idea how two yeasts perform compared to each other in the same beer.
I agree that this is likely a “genotype vs phenotype” issue. But there may be several factors all coming in to play together. Even if a STA+ yeast strain expresses the gene, it may be at a reduced rate, it may inhibited by other genes, the yeast may flocculate before it can consume much of the dextrins, etc.
In my experience with WY3711 (what I consider the most attenuative diastaticus strain), it takes an extra 7-14 days longer than a non-diastaticus strain would take to complete fermentation in a given wort. In that 7-14 day time frame it is only consuming the final 5-10% of gravity points. This leads me to believe that the additional fermentation from dextrin breakdown is a slow process. If a yeast flocs out and becomes quiescient before this phase is finished, then it will never hit the high attenuation levels we’d expect, despite being a diastaticus strain. We also have to factor in the other characteristics of the yeast as well. Imagine if Windsor had a STA+ mutant variety that was released from one of the yeast labs. In all likelihood we’d see attenuation numbers under 70%, but it would still technically be considered a diastaticus strain.
Amen to all that!
Technically, amyloglucosidase (a.k.a. glucoamylase or 1,4-alpha-glucosidase) is diatase because diatase is a complex of enzymes that also includes alpha-amylase, beta-amylase, and limit dextrinase. Glucoamaylase will break down starch in addition to dextrin and other higher-level saccharides including maltotriose. It is one of the enzymes distillers use in their mashes, which consist of mostly unmalted cereal grains. The amount of malt a local rye whiskey distiller adds to their grist during gelatinization is akin to adding malt to a cereal mash to reduce gumminess and make the mash easier to pump.
Below is a link to a publication on STA1 gene expression by Kristoffer Krogerus (a.k.a. Suregork). It explains why some STA1+ strains are not as superattenuative as others. Kristoffer believes that a 1162 base pair (bp) deletion that contains an upstream activation sequence and transcription factor binding site is responsible for some STA1+ yeast strains not expressing the gene (i.e., STA1 is in their genotype, but not their phenotype). Enzymes are protiens that act as reaction catalysts, which means that they are encoded via gene-based transcription. If I understand Kristoffer corrently, this bp deletion prevents the encoding of glucoamylase even when the STA1 gene is present.
So the official answer from Imperial is in line with Sacc’s linked article. STA+ expression varies by strain and not all STA+ strains exhibit the superattenuation.