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-   -   Strange smelling fermentation (http://www.homebrewtalk.com/f163/strange-smelling-fermentation-200093/)

RyanN 10-11-2010 02:39 PM

Strange smelling fermentation
Last week I cultured some yeast from 3 bottles of Bell's, 2 were Oberon and 1 bottle was Two Hearted. The culture was small and it was stepped up one time before I refrigerated and stored in a jar. This past weekend I decided I would use this yeast on a Two Hearted clone I was making. I made a starter (1.5L) and within 24 hours it had taken off pretty well, by the time my wort was chilled it was at high krausen (30 hours). I smelled the starter before pitching it and it smelled a little hot and a little buttery. I didn't think this was a huge deal since it was fermented pretty warm and I assumed that when the wort was fermented at a cooler temperature this smell would go away. The wort started fermenting within 12 hours and within 24 hours it was going pretty good. Now the entire room this beer is fermenting in smells buttery/almondy, you cannot smell hops at all (4 oz. in wort)? So here's what I'm thinking the possible problems could be.

Started was infected by wild yeast... .although I was pretty good with sanitizing.

Starter was stepped up too quickly causing stressed yeast which produced a lot of diacetyl

Phenols possibly created by too warm a starter ferment (80 max)

I'm worrying for no reason

I'd really like some opinions on what's happening here and what the possible outcomes might be.

Thank you.

hmmmbeer 10-11-2010 04:12 PM

I've never experienced this before but from the sounds of it, this beer could turn out amazing! Sounds like it could turn out creamy on the taste buds??? At this point, I can't see you being able to "correct" it so best guess is to just keg/bottle it and cross your fingers it turns out amazing!

Bensiff 10-11-2010 04:42 PM

The greatest likelihood for infection is from the yeast, especially if you are confident in your sanitization practice. Infection of gram positive bacteria such as pediococci and lactobacillus can result in diacetyl production. If this is the culprit you will get some obvious taste defects above and beyond butter. Further contamination may come from respiratory deficient mutants which have a decreased ability uptake diacetyl post fermentation and would be more likely found in strains that have undergone multiple pitches.

I don't know of an avenue for stress to produce diacetyl.

Too warm a fermentation is likely the reason for the hot alcohol.

Off the top of my head that is what I can think of. Make sure to give your beer plenty of time on the yeast during the stationary phase. The yeast will remove the diacetyl produced at this point to a point of saturation. If too much diacetyl was produced the yeast will be unable to clean it up. I would agitate the carboy during this phase to get the yeast back into suspension to maximize the reduction. As well, in the future consider using a quality yeast nutrient, especially when attempting to work with bottle dregs.

RyanN 10-11-2010 08:29 PM

Bensiff, I'm not sure I completely understand what your saying? Are you saying that the yeast themselves do not produce any diacetyl and if diacetyl is present it's due to infection, and if there is an infection it was most likely transferred to the starter wort by the bottled yeast? My understanding of what Palmer says makes diacetyl production possible by either infection or long lag time (I assumed that meant under pitched)? Since I sanitized thoroughly I assumed the yeast caused the diacetyl because they may have been under pitched? If yeast can clean up diacetyl wouldn't it be beneficial to add yeast along with some sugar at the end of fermentation to clean things up further? Clearly I do not fully understand fermentation and how yeast work, I'm trying though. Also, I did use a yeast nutrient, I forgot to mention that in the original post.


Diacetyl is most often described as a butter or butterscotch flavor. Smell an unpopped bag of butter flavor microwave popcorn for a good example. It is desired to a degree in many ales, but in some styles (mainly lagers) and circumstances it is unwanted and may even take on rancid overtones. Diacetyl can be the result of the normal fermentation process or the result of a bacterial infection. Diacetyl is produced early in the fermentation cycle by the yeast and is gradually reassimilated towards the end of the fermentation. A brew that experiences a long lag time due to weak yeast or insufficient aeration will produce a lot of diacetyl before the main fermentation begins. In this case there is often more diacetyl than the yeast can consume at the end of fermentation and it can dominate the flavor of the beer.
I smelled the fermenting before I went to work this morning at 4:30. I just got home about an hour ago and the fermenting beer now smells pretty normal...any ideas why that would be? It seems pretty early in the fermentation for the yeast to be cleaning up but maybe I'm wrong?

Thanks for the replies!

Bensiff 10-11-2010 11:45 PM

I was answering your thoughts down the list. I was saying that you probably didn't get an infection...I think people like to jump to that conclusion whenever something is wrong, but it is often the result of something else. However, if it is an infection, you sanitized well, and are usually a bottle claimed culture I was saying that would be the likely source.

Yeast produce diacetyl as a byproduct of making ethanol, so that is not what I was saying...just that some mutant strains of yeast that can develop with multiple generations become incapable of cleaning the diacetyl out of the beer after it is produced. If your yeast are healthy they will do a good job of taking care of any diacetyl they produce so I wouldn't start thinking about abstractions such as adding yeast late in the fermentation just yet. Some strains simply produce more diacetyl than others so keep that in mind. If it smells like its less it is probably the yeast starting to break down the diacetyl and reabsorbing it...so I wouldn't worry too much, see what happens.

RyanN 10-11-2010 11:56 PM

Thank you for your explanation. I'll definitely post back when I give this beer a try.

RyanN 11-11-2010 10:34 PM

Most likely a dumper
I'm not sure I want to try this, it just smells really off? Post fermentation these bubbles popped up which I do not have when using Safale US-05. I'm starting to think this batch is infected....maybe wild yeast? The smell is not horrible, it's just not right either....buttery chemical smell. Should I secondary this mess and see what happens? FG 1.010.


Bensiff 11-12-2010 05:05 PM

Is the black something mixed into the yeast or is it just dark because the beer is showing through open spaces?

Ichthy 11-12-2010 05:09 PM

Looks like yeast sitting on top of the beer. Just sample it and see what happens.

Revvy 11-12-2010 05:15 PM

Looks ok to me...Don't dump....see it through. You should never dump a beer until you've seen it through the entire process. Does it taste sour??? If it doesn't don't go by looks or smells. Fermentation is often stinky and ugly and perfectly normal.

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