Stuck fermentation vs lower attenuating yeast strain

Hi all, I wonder if anyone knows the answer to this question. I currently have an amber ale (extract + steeping grains) in secondary, after 20 days in primary. I used WLP001 with a 1.5 L starter, and it fermented from 1.052 to 1.017, which means I got 67.3% apparent attenuation. Obviously this is a fair bit less than the expected 73-80% attenuation White Labs advertises. But this got me thinking: is there a major difference between a stuck fermentation with a highly attenuating yeast like WLP001, versus a more complete fermentation with a less-attenuating yeast like WLP002? I know there will be flavor differences do to the different esters etc the two strains might give, but I'm just curious how much the sugar profiles would differ between the two scenarios.

Mark

Post recipe. I'd be willing ot bet 1.017 ia right on for WOP001 vs. a lot of extract IPA's.

The recipe is just 8 lb LME and 1 lb crystal 60. I'm not necessarily too surprised by the 1.017 FG; I'm more curious about the theoretical differences between two identical beers, one fermented partially by a more attenuative yeast and the other fermented more fully by a less attenuative yeast. Does that make sense? This is only my third batch and I'm just starting to learn more about yeast and trying to figure out what strains might get me the flavors I want.

Which brand LME? They vary, from manufacturer to manufacturer, in their level of fermentability. Remember, someone, somewhere, had to mash that extract. How that mash was conducted, and what the grainbill looked like, is perhaps the largest player in the kind of attenuation you see.

It's from MoreBeer, but that's not the point. The question is a thought experiment (or possibly there are data that answer the question). If a fermentation with a highly attenuative yeast ends up under-attenuated (compared to the published value), does it leave behind the same residual sugars and flavors as a normal fermentation with a yeast that has a lower apparent attenuation?

CraptainWirtz said:

It's from MoreBeer, but that's not the point. The question is a thought experiment (or possibly there are data that answer the question). If a fermentation with a highly attenuative yeast ends up under-attenuated (compared to the published value), does it leave behind the same residual sugars and flavors as a normal fermentation with a yeast that has a lower apparent attenuation?

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I believe it will be primarily driven by the FG. If both yeast strains end up at 1.015 for instance, I doubt there will be a disernible difference in residual sweetness. There might be flavor difference that is driven by the yeast strain however.

While I can't answer the question completely or with any great authority, I can say (in part due to the clarification you provided - thanks for that!) there might be a difference in residual sugars. The largest difference between strains that attenuate very highly from those that do not is the yeast's ability to ferment di- and trisaccharides (flocculation characteristics being the other major player, but that doesn't exactly seem relevant here). It is my understanding, though I may be wrong on this matter, that yeast tend to ferment the monosaccharides first before moving on to the more complex sugars, which take extra work as they need to be further broken down (which takes enzymes and/or other compounds that the yeast must produce, some strains being better able to produce these compounds). So depending upon where in the process of fermentation everything is halted, there may be a difference in the amount of complex sugars.

I would have to think this would affect flavor. The larger sugars are not as sweet as simpler ones, but they still generally register as vaguely sweet, I believe (even lactose is somewhat sweet, I understand, and that is too complex to be fermentable by sacc.). I believe the more complex sugars also aid in the perception of body.

The other matter to consider is that if fermentation is halted (say by crash cooling) partway through the process, the yeast will not go through their usual routine of preparing for hibernation, so to speak. This process includes all kinds of chemical reactions that affect flavor, like cleanup of diacetyl and other compounds created during the earlier phases of fermentation. By not going through this cleanup process, esters and other compounds may remain at levels they otherwise would not, had fermentation takes its more typical course.

That's not much, but I'm pretty confident all that is correct. I hope it's helpful for your thought experiment. It is an interesting question. I suppose a lot of it comes down to why the more attenuative strain did not achieve its usual level of fermentation, and at what point it stopped. I certainly can't speak to all the variables that might affect this process, unfortunately. I'll have to keep up to see if anyone else has more to add.

Thanks for the responses so far. It seems reasonable that residual sweetness equals residual sweetness regardless of how you got to the FG. I guess another way to think about it is, why are less attenuative yeasts less attenuative? Is it just that they poop out earlier than other strains, or are there certain types of sugars they metabolize poorly? (edit: derp - you addressed this point directly, GuldTuborg. Guess I need to work on my reading comprehension!)

I was originally thinking of doing a pale ale with Wyeast's London ESB yeast for my next batch because I like a maltier beer, but if this high-ish FG indicates that I don't get very good attenuation of this extract, I'm starting to second guess myself. I don't want it to be too sweet. My last beer with MoreBeer's extract (a stout) ended up at 1.024, and it really doesn't taste that great.