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Ferm Temp and off flavors question

Dear yeast experts:
I am beginning to gain a deep appreciation for temperature control during primary fermentation. (At the same time, I am quite intrigued by the Belgian habit of cropping at high Krausen, and reintroducing the primary yeast at bottling to achieve higher attenuation). My question involves the off flavors that come from primary fermentation at too high a temperature. Not the fruity flavors, but the ones that taste like solvent. I have read many sources that deal with the topic of preventing these flavors, but I would like to know…will any amount of aging (or any other procedure) get rid of them? Do they fade over time?

Thanks for your input.

Rob

You are referring to fusels and they do not fade. During the conditioning phase, the yeast will convert as much of the fusels into esters (the fruity flavors as you put it). Once the yeast are finished and drop out, you’re left with the final product. The esters and phenols may fade over time, but the fusels left over from conditioning will remain since the yeast are no longer converting them. It is possible to add actively fermenting yeast (starter at high krausen) to a beer to get more conversion of fusels but it’s much, much easier to just keep temps down during primary fermentation.

ah, the fusel oils. aka ethyl acetate.
hmmm…I believe I still have some bottle fermentation happening, the gravity reading at bottling was not down to where I anticipated it being, and in two samples separated by a week, there was a noticeable difference in carbonation. Hopefully the yeasties are still alive and converting. Otherwise, it may just be a dumper.
bummed at the prospect.

Bottling early, before fermentation is over, will cause fusels to remain in the beer. The yeast convert fusels only after consuming all the sugar.

But I’d be more worried about your bottles exploding due to continued fermentation.

what about the priming sugar, then? wouldn’t that feed them into converting to alcohol, then consuming existing fusels? I don’t know, I’m just wondering. 3 weeks so far, no exploded bottles. I am keeping a close eye out for contaminated bottles though (via broken seal).

[quote=“The Mad Zymurgist”]Dear yeast experts:
(At the same time, I am quite intrigued by the Belgian habit of cropping at high Krausen, and reintroducing the primary yeast at bottling to achieve higher attenuation). My question involves the off flavors that come from primary fermentation at too high a temperature. Not the fruity flavors, but the ones that taste like solvent. I have read many sources that deal with the topic of preventing these flavors, but I would like to know…will any amount of aging (or any other procedure) get rid of them? Do they fade over time?

Thanks for your input.

Rob[/quote]

Say what? AFAIK, the reintroduction of yeast is for carbonation, not to achieve higher attenutation. If there was enough fermentation to really do that, the bottles would likely explode.

As far as fusels, I read a paper by Dr. Bill Pengelly many years ago about how fusels will age out into esters. That’s been my experience. I can’t tell you how long it might take because it varies based on the beer and it’s particular problems. But I have taken advantage of the phenomenon a few times and it does happen.

You don’t use enough priming sugar for any appreciable amount of fermentation.

Denny:
I don’t know that for certain, but I was basing the statement about higher attenuation on the fact that most Belgian (abbeys, Trappists, and copy-cats) tend to claim they are obtaining 88% and higher attenuation, while I have not found a commercial yeast, Belgian or otherwise, that makes anywhere near that claim.
I would expect explosions, also, but I also figured there are folks who have been brewing centuries longer than I have who know a lot more than I do. Of course, I could just be misinterpreting the data.

Glad to hear about the eventual degradation of fusels into esters. This is a sort of ale I would expect to have to age a good 6-12 months for best flavors anyway, so maybe I’ll just let it set and see what happens.

In the meantime, I have an Altbier that should be ready to tide me over in about a month, and it’s already mouthwatering.

Thanks again!

p.s. currently reading White & Zainasheff: Yeast. Wonderful book!

Denny:
further research has elucidated this attenuation issue. Apparently, I am under-controlling more than one variable. Temperature can rise higher than what I would normally be comfortable with, if the yeast count is high enough (I suppose I need to start counting my yeast cells when pitching) AND they are adequately aerated (although I have discovered that it IS possible to over-oxygenate!). In fact, higher temps with adequate yeast count seems to be how the Belgians obtain such high attenuation numbers, without adding fusels (but esters are an integral part of the product). Oh, and that’s not all, protein rests during mash are critical for assuring the yeast have proper nutrients to use without leaving behind unwanted byproducts.
You know, when I first started this years ago, I dreamed of doing it as more of an art. But I suppose practicing brewing more as a science has its positives as well.
I appreciate the input, and I hope that if I’ve missed anything you’ll let me know.

Thanks again!

[quote=“The Mad Zymurgist”]Denny:
I don’t know that for certain, but I was basing the statement about higher attenuation on the fact that most Belgian (abbeys, Trappists, and copy-cats) tend to claim they are obtaining 88% and higher attenuation, while I have not found a commercial yeast, Belgian or otherwise, that makes anywhere near that claim.[/quote]

Keep in mind that yeast is only a small part of the puzzle. The attenuation rating of yeast is really for comparing one yeast to another in a standard wort. It’s not really an indication of the attenuation you can expect. That’s really dependent on the fermentability of the wort. I can get anywhere from 60-90% with the same yeast depending on the wort.

I’m afraid I may have to disagree with some of the statements in your follow up post. Have you read BLAM? I consider it to be the definitive work on brewing Belgian styles. From reading it, I haven’t found many breweries that start their fermentations at high temps. It appears that the usual method is to start in the 60s and then let temps rise. By doing that you limit fusels and esters, which are usually formed early in fermentation. And I’m also not aware of the reasons you state for a protein rest.

I’m reading BLAM now (fascinating!), and you’re right, the pitch is at 68, then allowed to rise. I see what you mean, that fusels form early if you let them, but by letting the temp rise later they can be avoided.
The protein rest statement is a beginner’s distillation of what I’ve been picking up in Yeast (White and Zainasheff) - my other casual read just now. This book is a bit over my head, so I plan to absorb what I can now, and reread it after some more experience to see what else I can take away. The protein rests can control what enzymes are available and in what quantities for the yeasties, thereby gaining a small degree of control over the final taste the yeasties produce (by controlling their food source, you can control their byproducts). Obviously the grain bill and adjuncts also contribute to the control of the available food supply, but so does oxygen and pH…I suppose I can make this as complicated as I want to, if I want to…
Again, above my pay grade, but I am fascinated by the education.

From my experience, a protein rest is almost never needed and can be detrimental if done wrong. What people used to get from a protein rest is now done by the maltster during the malting process. I haven’t done one in years.

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