Yeast Blow Off=Acetaldehyde???

[crupp]

All,

A friend of mine asked a question that I could not answer. We’ve both been having acetaldehyde problems. My acetaldehyde problems have been sporadic, so I’m assuming that it had to do with 02 ad pitching rates as I think that I’ve figured mine out (haven’t’ had a problem in 4+ brews). He (on the other hand) has still been struggling, so we’re still trying to get to the source. We have both been pitching with the mrmalty.com recommendations, adding pure 02 and allowing the beer to sit on primary for 3-4 weeks in order to allow the yeast to do its thing. We’ve also been raising fermentation temps up towards the end of fermentation in order to help clear up acetaldehyde. We are at the point where we are starting to think that he may have a bacterial problem.

He has noticed that he has had significant blow off on all of his acetaldehyde beers (I have not), so he was wondering if it is possible to lose too much yeast during the blow off, which would leave the fermenting wort with an insufficient amount to help clean off “bad” fermentation byproducts. At first I said no because I figured that a blow off would mean that there is a vigorous fermentation. But then I though for a while that it is during the initial fermentation where byproducts such as acetaldehyde are developed (and when most blow offs take place).

I don’t know…I think we’re grasping at straws. What do you guys/gals think?

[Nyakavt]

I've had acetyaldehyde show up exactly twice, and both times it was the first pitch of lager yeast, and both times it required extended warm conditioning to eliminate it. It seems for me to be a yeast viability issue, as subsequent batches with the same aeration method did not have the problem. Is this with liquid or dry yeast? Are you ever repitching, and if so does the acetylaldehyde show up in the repitched beer? Is there any pattern to the beers that have the problem, gravity or yeast strain or whatever? What method are you using to grow the yeast for starters (stir plate, simple, etc.)? You can try measuring the slurry from the starters to get a rough idea of the cell count and see if you are actually growing as many cells as you think.

For diacetyl reduction at least (you never really hear much about acetylaldehyde reduction, but I assume the methods are the same) they say to raise the temp just as the yeast starts to slow down, not after it has already stopped. Is this when you raise the temp? The blowoff idea makes some sense, but it's hard to say that this is the cause without knowing how much yeast is left in the beer. I suppose you could measure the slurry volume of the blowoff and the rinsed slurry volume in the bottom of the fermenter to see what % of yeast you are losing to blowoff.

[KimJongAle]

If he's having blow-off that often, perhaps it's time to look into a slightly larger fermentor. I hear the Blichmann 42 gallon conical is quite nice

[ApresSkiBrewer]

Give us some more details... carboy sizes, yeast strains, starter (yes, no, big, little)... Also, what are your lag times?

For instance, if you top up a 5g carboy to the brim, and have a very hefty blow off, you will definitely loose a significant amount of your 'best' yeast for sure. This might lend to the problem. Otherwise though, it seems like you're doing everything else right to try and reduce the acetaldehyde.

Nyakavt is absolutely right. Start your temperature bump when the krausen just begins to fall, in fact... after you've hit your max airlock activity and high krausen, you're not getting any more (or at least very little) yeast growth (and therefor any/minimal ester production) - so your fermentation temp is much less of a concern (don't let it cool down, and don't go wild... but you know what I mean). Bump it a solid 3-4ºF, and you won't see any ill affects (with viable yeast at the proper pitching rate). This should help give the yeast the metabolic boost they need to clean up that intermediary to ethenol.

More importantly, do you use any yeast nutrients? If your wort is deficient in Zinc, your yeast will stuggle in the reduction of Acetaldehyde into ethanol (the enzyme is alcohol dehydrogenase, with a cofactor of Zn) Try some yeast nutrients rich in zinc. That might be all you need to do.

If you are using zinc rich supplements, then... we'll think of something else to blame!

[crupp]

WOW…where to start. It has actually been all over the place. I can speak to my problem, so we’ll start there…I can honestly say that I've lost close to 80 gallons due to acetaldehyde. All size batches, multiple fermenters, different yeast, different yeast preparation, different fermentation times, and different 02 levels.

Is this with liquid or dry yeast?

First couple of times was Safale 05. Dry, did not rehydrate. I have also gotten acetaldehyde from liquid yeast. I use mrmalty for all of my starters and do my best to get a close to the recommended volume as possible. I have also gotten acetaldehyde with stir plate starters, non stir plate starters, and slurry from some of the local breweries.

Are you ever repitching

no

Is there any pattern to the beers that have the problem, gravity or yeast strain or whatever?

Honestly, the only pattern I've been able to come up with is 02. I've cut my 02 down to 30 seconds and the problem seems to have gone away...I'm not convinced that's why it went away, but it's what I've noticed. Yeast has come from multiple homebrew shops as well as slurry from local breweries. It is (for the most part) some form of California Ale yeast; although last time it was 002.

Give us some more details... carboy sizes

I always have good head space. I use 6 or 6.5 gallon carboys, a 12.5 blichman conical, 15 and 25 gallon hobby beverage plastic fermenters.

Also, what are your lag times?

Normally between three and eight hours.

I think that Nyakavat is on to something with raising the temp towards the end of active fermentation. I think that i'm in a decent range of temperature towards the end of the active ferment, but I could be wrong. I’ve also started keeping the beers in primary for an extra week(normally 4 weeks total) before racking to keg.

The kicker is that I have batches in between where I don't get the acetaldehyde...I'm at a loss. I've been pretty luck for the past few batches, but worry about it coming back. I've just picked up a few 25 gallon stainless kettles and I do not want 20 gallons of granny smith!

Thanks in advance for the assistance.

[ApresSkiBrewer]

You ever consider just tracking down 001 - 1056, and getting away from saf 05? I've heard that strain can be 'apple-y' on it's own... but I've never brewed with it.

[ajdelange]

First, what may seem to be a stupid question which I only ask because I've run into confusion over the 2 before but people often confuse diacetyl and acetaldehyde (all those c's, y's, l's and a's I guess). Acetaldehyde tastes like apples (low concentration), rotton apples, higher and formaldehyde (higher still). Note: went to a wedding last weekend where they had a pony of Coors (which has not passed my lips in years) which tasted so much like apple juice I thought (keg was covered with ice so I couldn't see what it was) it must be Bud (which hasn't passed my lips for years either). That's acetaldehyde and is obviously a product of yeast metabolism and is quite normal as both AB and MC are reasonably skilled at brewing beer. Diacetyl is caramelly at low levels, buttery at higher and just nasty rancid at high levels. So the question is "What does this taste like?"

If it tastes quite apple like (the sweetness of the corn plus the apple of the acetaldehyde in the Coors really did resemble apple juice) that can be normal and the fix is to use a yeast strain which is not so much an acetaldehyde producer though any strain should be given the opportunity to reabsorb acetaldehyde by proper management as has already been discussed in this thread. If the aroma/flavor gets into the rotton apple/aldehydic range then the problem is most probably infection by a strain of bug that produces lots of acetaldehyde (particularly Zymomonas).

One is tempted to suspect that an unusually violent fermentation might involve organisms other that S. cerevisiae but I am happy to say that I have no experience (touch wood) with Zymomonas.

[thatguy314]

Just follow up. Acetaldehyde is specifically green apple / granny smith. You can get acceptable apple esters (ethyl hexanoate in particular if I'm remembering correctly, but the other major esters can have fruity/apple like qualitites, not not the same sharpness)

Acetaldehyde (AJ correct me if I'm wrong) is mainly produced as an intermediate in alcohol production. So you primarily get acetaldehyde production from in complete fermentation. Therefore, make sure you're fermenting at an appropriate temp (too cool and it might not finish off, too warm and you'll get a racing ferment and it also might not finish off). Also from over/underpitching.

My 3 recommendations:
1) Pitch an appropriate amount of yeast (sounds like you at least are doing that)
2) Ferment at an optimal temp, and raise it a few degrees higher as fermentation is finishing up
3) If you've still got some diacetyl left at the end, you can make a starter from your yeast and get it to high krausen and pitch it back into the beer. The actively fermenting yeast may be able to clean up a lot of the off flavors. This is a similar process that many German breweries do by Krausening. Similarly bottle conditioned beers should clean up a bit if they're kept at an appropriate temperature, though it will probably not be complete unless the acetaldehyde was at low levels.

Even if you are confusing acetaldehyde and diacetyl, the fixes are very similar.