Author Topic: Fusel alcohols revisited  (Read 3695 times)

Offline surfin_mikeg

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Fusel alcohols revisited
« on: October 05, 2012, 07:51:00 PM »
I'm on the opposite side of andrew000141's "fuel alcohol" thread where I want a strong ester profile for saisons and am just learning about temp control.  I just brewed a honey-orange saison (mash at 150 deg, WLP566, 6%, 40 ibu), and I upgraded the fermentation heater from 50W to 200W without testing first.  The high temp setting says 89 degrees, so I went with it. 

The next day after pitching I checked, it was krausening at 97 degrees.  Tasted horridly awful with fusels, and it fermented out at 85 degrees.  6 weeks later (w/ rack & bottle at ~60 degrees), the majority of fusel notes are gone and should be quite fine in a month or so.  No headaches.

I'm not tasting a lot of esters yet - does it help if the beer is mashed at a lower temp?
How about fatty-acid content to promote esterification - does honey help in that regard?

Any other tidbits?

Cheers.
Devil's Slide Brew Club

Offline paul

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Re: Fusel alcohols revisited
« Reply #1 on: October 05, 2012, 10:25:58 PM »
I haven't used that particular saison yeast, and I'm not familiar with any correlation between mash temp and esters.  But the description for WLP566 suggests that it should result in significant esters.  I wonder if your high fermentation temp actually exceeded the ideal range enough to either suppress esters formation, or enough that fusels or phenols are overwhelming the esters?

Next time, I'd suggest starting fermentation near the low end of the temperature range, then ramp it up towards the top end over the next 2 or 3 days.

You also might want to play with pitch rate and oxygenation levels.  I've read conflicting information about this.  Some brewers coax esters from their yeast with low pitch rates and high oxygenation, while others do the opposite.  I recently tried a high pitch rate and lower oxygen for Belgian Blonde and got some decent esters from WLP500.  I haven't used this yeast before, so I'm not sure how much the pitch rate mattered.  I may try a low pitch next time.

Offline nateo

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Re: Fusel alcohols revisited
« Reply #2 on: October 06, 2012, 07:22:41 AM »
I'm kind of an idiot, but here's my understanding: Acetyl-CoA is acetate and Coenzyme A. The Coenzyme breaks sugar down into pyruvate, which can be turned into acetate and attached to the Coenzyme to form acetyl-CoA. In the presence of oxygen, the acetate can be broken down into CO2 and water. If there's no oxygen, the yeast has to turn the acetate into "something else" to get rid of it. The "something else" is yeast byproducts.

It's my understanding that if the yeast is using acetyl-CoA for growth, it can't be used for ester production. I'm not sure exactly how that works, but it squares with info from Neva Parker (WL) and Dr. Cone (Danstar) that high pitching rate = less growth = more esters.

I think there's a strong strain-dependent variable here, because Wyeast, for instance, found that overpitching their weizen strain meant basically no banana esters were formed. So there's a lot of anecdotal evidence that seems to contradict the "scientific" explanation. Although, I think the composition of your malt and your wort should have a pretty big impact on the types of flavors created during fermentation, but hardly anyone talks about that, outside of doing a ferulic acid rest for weizens.

FWIW the best Belgians I've made have been massively overpitched. I've found that using dextrose gives different yeast character than using sucrose or levulose. I used to use a lot of table sugar when making my Belgians, but I've been happier with the results from dextrose. I haven't done any true ABX comparisons to verify, so take that with a sack of salt.
« Last Edit: October 06, 2012, 07:25:04 AM by nateo »
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Offline surfin_mikeg

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Re: Fusel alcohols revisited
« Reply #3 on: October 06, 2012, 03:33:57 PM »
Thanks for the reply Paul & Nateo, that gets me going in the right direction.

How does a homebrewer control for low oxygen rates?  Seems like that's a controlling factor (as compared to pitch rates) along with glucose (via dextrose) & some fusel production. 

The chemistry terms are appreciated; I'm finding a lot of reading material by searching on https://www.jstage.jst.go.jp.

I'll give it another try.  Going between IPA's (hop + water science), Pilsners (water + lagering technique), & Saisons (fermentation chemistry) is like working through a college course in homebrew (not a bad thing ;) )

Cheers!
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Offline paul

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Re: Fusel alcohols revisited
« Reply #4 on: October 07, 2012, 08:31:53 AM »
Good question on the oxygen rate, since we can't measure it as home brewers.  My understanding is that just shaking the carboy maxes out at about 8 ppm oxygen.  I think this is generally regarded as barely adequate for all but lower gravity beers.  So to me, low oxygen consists of just shaking the carboy, and perhaps not as thoroughly as I would normally do.  If I want high oxygenation, I'll hit the wort with some pure O2.