How to get rid of acetylhyde?

[Lynchy217]

Hi,

I brewed a Chocolate milk stout on May 28th. I racked it to secondary about 2.5 weeks ago. At that point, it was a bit sweeter than I wanted, but tasted pretty good. The primary fermentation seemed to be done, but I had just broken my hydrometer, so I wasn't able to get a reading. I moved it to secondary onto 3 oz of Cacao nibs, where it has stayed for 2.5 weeks.

Today, I moved the beer to a keg in hopes of having it to serve tomorrow to get some feedback from a few friends. While I was racking to the keg, though, I got a wiff of acetylhyde. I poured some into my hydrometer tube. It came out with a FG of 1.018, about in line with expectations. I tasted it, and the acetylhyde is even worse than I initially thought. I'm interested in entering a version of this beer in a competition in the fall, so I want to brew it a few times to tweak the recipe. I've read that yeast will eat the acetylhyde over time, but I was wondering if there's anything I can do to reduce it faster. Since I racked to the keg, there aren't a lot of yeast cells in the beer at this point, so I want to help them along as much as possible. I put the keg in a temp-controlled keggerator at 68 degrees, since I read on a wine forum that that's the best temperature for yeast to eat acetylhyde (though I'm sure this varies with yeast, and given the differences between wine and beer yeast, probably means nothing). What else can I do? Should I pitch more yeast? Are there any tricks for getting rid of the off flavor faster? What can I do in the future to avoid the presence of this off flavor in the first place?

Thanks all!

 

[passedpawn]

Popular theory is that time, and new yeast, will solve the problem. ACE is a intermediate product of fermentation, and thus more healthy yeast will fix.

My experience is the best solution is dumping it. With high-ABV beers, yeast won't get along too well anyway.

 

[Lynchy217]

This is far from a high ABV beer, though. From my calculations, it's about 4.6%. If healthy yeast is the answer, I can pick some up tomorrow. I wasn't sure how effective that would be, though.

 

[mbobhat]

How long did it sit in primary? Racking too early can cause this. Also, oxygen introduced can also cause this. If it's oxygen, it can get worse by producing acetic acid if infected. Thus you'll know pretty soon if it's a dumper for sure

 

[Lynchy217]

It was in primary for about 2 weeks. The fermentation was weird from the beginning, too. I saw no Kraussen at all, but the airlock was going. I did a taste test between the primary and the secondary, and it tasted fine, so it didn't seem like it was infected then. In the secondary, I did notice that I had a decent size yeast cake under the nibs, which is a little weird for secondary from my experience, so my best guess at this point is still acetylhyde from removing from the primary too early.

 

[Queequeg]

I keg most of my beers after 2 weeks. Time on the cake isn't the issue.

I would look to yeast health, pitch rate and fermentation temperature.

As for you the beer in hand, it will clean up slightly but ultimately you'll always be able to taste it.

The only option is to use Brett. Or bin it.

 

[Duffman870727]

For your future brews, to address this issue, what kind of yeast are you working with? A proper size pitch of healthy, viable yeast will chow through fermentation and fully clean up after themselves in 2-3 weeks (Kölsch was bred to leave behind some acetaldehyde however). Unless you are brewing lagers (extended aging) I don't see any benefit to a secondary transfer, it is fine to leave the beer on the cake the whole time.

If your yeast wasn't healthy (old generation, stored a long time without food, etc..) or you underpitched, the cells will just get tired at the end of fermentation and give up eating the bigger sugars and won't fully clean up after themselves. You have to be pro-active about this and pitch the proper amount of healthy yeast, every time.

If you're not sure if the beer is ready to transfer off the cake (if you insist on secondary) or package, pull a sample and do a forced diacetyl test. There is no real test for acetaldehyde in beer (other than sensory, if you are sensitive to it) but it is linked to diacetyl and gets cleaned up at the same time. Removal of all diacetyl from the beer by the yeast is a good indicator that the acetaldehyde has been cleaned up as well.

Acetolactate (diacetyl precursor) is odorless and flavorless until it breaks down into diacetyl, which it will do over time if any exists in solution in the packaged beer. You can force any acetolactate to convert into diacetyl by heating the sample to 140F-158F for 20 minutes. Compare the forced sample to a regular sample, there will be one of three results:

i) Diacetyl detected in both samples means that beer is not finished fermentation, healthy yeast will have cleaned the beer of all diacetyl when fermentation is complete.
ii) Only heated sample produces diacetyl. This means that fermentation is near completion. The yeast are cleaning up the diacetyl in the beer, but some acetolactate precursor still remains to be broken down and re-uptaken.
iii) Both samples diacetyl negative. All precursor has been broken down, and all diacetyl has been taken up by the yeast. This beer has completed fermentation.

Allowing the temperature to "free-rise" when you're at about 80% attenuation will help the yeast re-uptake the acetaldehyde and diacetyl. The colder you can ferment primary, the more you'll suppress production of these compounds, but yeast are "happiest" at around 80F, so allowing the temp to rise near the end of fermentation removes some stress from the yeast and they will be able to do a better/faster job of cleaning up.

Hope that helps.

 

[BBBF]

Krausening it might work. I was in a very similar situation with a stout. I kept it around for a year and it didn't clean up. I eventually brewed another stout and in a last attempt to make something out of the acetyllhyde batch, I racked it onto the fresh yeast cake and added a gallon of fresh wort. This reduced the acetyllhyde, but I'm not sure it's worth making another batch of beer to "try" to save the first batch. Unless you feel like experimenting.