Technical question about fusel alcohols...

I know that the chemical processes that take place during “aging” aren't completely understood, but has anyone ever done the simple experiment of determining the concentration of propanol, butanol, and other higher-order alcohols both at 1 month and then at 1 and 2 years from fermentation? This should be a very simple thing to do for anyone who has access to a university chemistry lab.

Also, if the C-C bonds of higher-order alcohols get broken so that they result in ethanol, why doesn't the C-C bond in ethanol break resulting in methanol?

These are two great questions. I don't have the answers, but I'm interested if anybody else does.

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I've come accross 2 sources that point oppsite directions for fusels creation/aging requirements.

The first, found here(in the forums), and later the source in a web search said that more O2, more yeast, more degassing and more nutrient lead to more fusels.

The second was a pod cast (beersmith #20) with Curt Stock who makes award winning meads. He says he can get a mead drinkable in 8 weeks! His method? he adds nutrients in a typical step manor (1/4th each time), and down to 50% OG he actually not just degasses to remove CO2, but does a mild amount of areation. - again both are direct opposites. *Curt also mentions using Lavin k71 which is rated as a 'young wine yeast' most suitable for making quickly drinkable wines.

I think a 1 gallon experiment needs to be done with 1 gallon being done as method 1 recomends and then 1 as method 2. Controling as much as possible for other factors, I'd make them at the same time. I want to do this, but as usual need something - at this time fermentors.

As in Beer yeast are supposed to create fusels under 'stress' conditions, I'm a bit confused why #1 would be true, but then there are a lot of counter intuitive things out there, so why not. If I get this going, I'll post.

Searching the web for anything on the stability of fusels shows up nothing of much use, so unless there is a particular process or reaction occuring that is converting them to lower order alcohols, my guess would be that fusels don't age out at all, though maybe they "smooth" out their flavour over time much like the ethanol does which makes them less pronounced in the flavour.

Well, the flavor of butanol is the flavor of butanol. It doesn't “change” or “smooth” over time. I understand that the change in flavor of beverages during aging is the result of many (not well-understood) chemical reactions, but there are only two basic ways for the flavor of a specific compound (like butanol) to “smooth”. Either the butanol is chemically transformed to another compound, or other unrelated reactions create other compounds which mask the flavor of the butanol.

I do have two degrees in chemistry, but organic chem was not my specialty. I may dig up my old org chem textbook and see if it has the strength of the C-C bonds for various alcohols. It might be the case that the C-C bond in ethanol is stronger than those of higher-order alcohols because there are only two carbon atoms.

Still, it would seem to me that a simple gas chromatography analysis of a batch over time should answer the question of whether higher-order alcohols do indeed decay.

By smoothing, I meant your second option of other flavours masking them rather than the flavour itself changing.

OneCerebralSamurai said:

Well, the flavor of butanol is the flavor of butanol. It doesn't “change” or “smooth” over time. I understand that the change in flavor of beverages during aging is the result of many (not well-understood) chemical reactions, but there are only two basic ways for the flavor of a specific compound (like butanol) to “smooth”. Either the butanol is chemically transformed to another compound, or other unrelated reactions create other compounds which mask the flavor of the butanol.

I do have two degrees in chemistry, but organic chem was not my specialty. I may dig up my old org chem textbook and see if it has the strength of the C-C bonds for various alcohols. It might be the case that the C-C bond in ethanol is stronger than those of higher-order alcohols because there are only two carbon atoms.
Still, it would seem to me that a simple gas chromatography analysis of a batch over time should answer the question of whether higher-order alcohols do indeed decay.

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I would be inclined to say that this may be the case. Also, sterics may play a role. And doing GC on a batch over time sounds like a fabulous senior project for a homebrewing chem student! I wish I would have thought of that when I was in college (maybe I would have had I been brewing then).

Fusels do smooth out. They combine with acids to form esters through non-enzymatic reactions while aging. However, this process can take a long time with some batches.

Anything that causes faster yeast growth and faster fermentations rates seems to increase fusel alcohol production. However, the key drivers seem to be yeast strain (some can nearly produce an order of magnitude more than others) and temperature. And remember, the term fusels encompasses a lot of different compounds and each one is affected differently by the fermentation conditions - some may get produced more and some less. What's more, their impact on aroma and flavor is quite variable with some compounds being beneficial at lower levels, and odor-causing at higher levels. So all fusels are not bad, and some are quite important for aroma and flavor. We tend to lump them all together in discussion however, with the idea that they are all bad.

AC, there is nothing contradicting Curt Stock's results. You can make a mead that is drinkable in 8 weeks, especially if you use lots of berries, 71B yeast, and keep it sweet. DV10 is another yeast that is very low in bitterness for early drinking that can work. In a sweet berry batch, higher fusels are not necessarily a problem, just like in red wines, higher fusel alcohol levels are expected (when compared to whites).

However, if you are making traditional meads, high amounts of some fusels can really wreck your results leaving it burning hot and smelling like paint thinner. After that it may never age into what it could have been had it been managed better during fermentation.

OneCerebral, I'd love to see someone send some mead samples to the lab for fusel measurements as it would give us some really useful information to digest.

Medsen

Thanks Medsen. That makes more sense, because I couldn't figure out how C-C bonds would be broken during the relatively quiet conditions of aging. Alcohol → Ester transformation is much easier given that it's mostly O-H and C-H bonds involved, and those H+ ions bounce all over the place in an acidic solution.

So, I guess that's my answer. Fusel alcohols do not “break down”, but they really combine together to form larger esters which result in a smoother taste and better aroma (usually). I guess it's the imprecise language that was causing my confusion.

As for an analysis... there's got to be someone here who has access to a chem lab....

MedsenFey said:

Fusels do smooth out. They combine with acids to form esters through non-enzymatic reactions while aging. However, this process can take a long time with some batches.

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Medsen, are you aware of anything/any research as to what, if anything, can be done to speed up the process? If acids are part of the equation, would this make a case for adding acid blend to most any mead that finished hot; ie, would having more of this substrate speed up the process?

I don't know of any research on that question, but it is a good one. I once tried heating a very fusel-heavy batch in the way they do for a Madeira wine to see if that would speed up the clearing of fusels, but in my anecdotal experience, it didn't seem to make much difference. I didn't send sample for quantitative measurements, but my nose and taste buds told me quite clearly that it hadn't resolved the issue.

Well I did a google search on Fusels and the wiki page for fusel alcohol (http://en.wikipedia.org/wiki/Fusel_alcohol) mentions that Temps, lower ph's and yeast activity limited by nitrogen (so low FAN) durring fermentation.

This would get back to putting in the nutriants that Curt Stock mentioned. Also it would seem that if acid helps reduce the Fusel's over time, then degasing would be contra indicated as CO2 in water creates a mild acid.

ACbrewer said:

Well I did a google search on Fusels and the wiki page for fusel alcohol (http://en.wikipedia.org/wiki/Fusel_alcohol) mentions that Temps, lower ph's and yeast activity limited by nitrogen (so low FAN) durring fermentation.

This would get back to putting in the nutriants that Curt Stock mentioned. Also it would seem that if acid helps reduce the Fusel's over time, then degasing would be contra indicated as CO2 in water creates a mild acid.

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Degassing is still beneficial for a healthy fermentation, and therefore the reduction of fuesels in the first place though...you even mentioned it in the first part of your post (lower pH's).

I was referring more to the addition of acid blend *after* the fermentation was complete. My theory would be that "loading the deck" on the one side of the equation could help push that non-enzymatic reaction faster by providing more substrate.

It would make sense, and if true you could pick your acid to match the ester you want... Mmmm pear drops... Though I think that one involved something nasty so maybe not!

ACbrewer said:

Well I did a google search on Fusels and the wiki page for fusel alcohol (http://en.wikipedia.org/wiki/Fusel_alcohol) mentions that Temps, lower ph's and yeast activity limited by nitrogen (so low FAN) durring fermentation.

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From the scholarly papers I have reviewed, I'd say wiki has that wrong. Nutrients and rapid yeast growth promote fusel production, but that doesn't mean you should try to starve your yeast. If you don't feed your yeast properly, the sulfur odors and other byproducts from the under-nourished yeast will be far worse than the fusels produced by a healthy fermentation.

Esterification requires heat and a catalyst (acid), as well as being formed from carboxylic acids, not alcohols (unless vinyl chloride is added, which in this case is very, highly doubtful). The reaction is also highly reversible, especially in the presence of water.

Formation of Ethyl Esters of Tartaric Acid During Wine Aging: Chemical and Sensory Effects from Am. J. Enol. Vitic. 36:2:118-124 (1985). This is just one example of how an alcohol and an acid can combine to form an ester in wines.

MedsenFey said:

From the scholarly papers I have reviewed, I'd say wiki has that wrong. Nutrients and rapid yeast growth promote fusel production, but that doesn't mean you should try to starve your yeast. If you don't feed your yeast properly, the sulfur odors and other byproducts from the under-nourished yeast will be far worse than the fusels produced by a healthy fermentation.

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Well I'll put published papers with statistics over wiki, particulary on something like this. So moral is to properly feed the yeast, not to much, not to little. Brings on other questions about pitch raters, but I should start a new thread for that.

Hey guys,

I just brewed a batch that I'm pretty sure ended up with fuesel alcohol off flavours, but I have a question about whether that can include or increase bitterness.

I brewed a new recipe - NEIPA - turned out it was 10kg malt (5gal batch) instead of my usual 6kg, and I massively underpitched using only one vial of white labs Vermont ale yeast. I also didn't control fermentation temp and it probably sat at around 23-24c (75f). I also struggled to aerate it much pre pitching. So pretty much a lot of mistakes in one.

I spotted a hot flavour after it had fermented for about 10 days, and figured it's a drain pour. I just tried it one more before ditching and it left quite a long bitter taste - I used a small charge of bittering hops and everything else was hop burst after it had started to cool. Is this likely to just be a green beer flavour or could it be from the fuesel off flavours/stressed yeast?

Thanks!

Chris

Wasn't there something in the big rice wine thread regarding aging for cherry flavour development? Could that be the reaction mentioned?

Chris, don't drain pout that, rack it off the lees and just park it in a cool dark corner and forget about it for about 6 months, then re-sample.