Acetalaldehyde reuptake?

[ApresSkiBrewer]

I ran this question past JZ once, and he told me to warm it up and add an active fermenting yeast starter. It worked pretty well, although I don't think I ever got rid of all of it, but made it drinkable.

Yep. This is the common fix recommended for acetaldehyde in noticeable but not overpowering concentrations. Nearing the end of fermentation, a few degrees bump in temp (think D-rest) will also help the yeast clean up residual acetaldehyde to levels below taste thresholds. Some yeasts/fermentations may benefit greatly from this, obv. dependent on pitching rate/yeast viability/o2, etc. After log phase growth, temp control is still very important, but most ester formation is a function of yeast reproduction... my point being, temp control is absolutely vital during these stages, but as you approach your final gravity, again, a temp bump will help in reducing these compounds and help achieve maximum ADF.

I would bring it out to about 50-52ºF, pitch some krausened yeast (if you have some, even a different lager strain would be fine, IMO) or a small portion of an actively fermenting starter, and see what that can do.

I was unaware that acetaldehyde was so volatile though, so if you were brave and wanted to try an experiment... you maybe could warm it up a bit... and instead of just venting your keg as CO2 is coming out of solution, push at a VERY low pressure down your dip tube with your PRV open... and see if you could vent off by bubbling CO2 through the beer. It would be dependent on if you had enough head space in the keg to provide for some foaming... and if you are willing to beat some of those foam forming proteins out of solution for the sake of venting off the acetaldehyde.

^^^ Just a random thought... I've never heard of this being practiced/used as a method to reduce perceived acetaldehyde. Probably not worth the risk, but I thought I'd throw it out there.

I agree that time might do the trick... but if that's the case, I'd think it would take 6 months or more for you to get any sort of result. I don't have that type of patience, but maybe I should!

good luck,

[ajdelange]

...I'd think it would take 6 months or more for you to get any sort of result. I don't have that type of patience, but maybe I should!

With lagers (and, actually, with ales too) patience on this scale is often rewarded. Right now (not at this precise moment; the sun isn't over the yardarm yet) I'm drinking a Pils that I brewed over a year ago (alas I'm on the last part of the last keg) and one I brewed last August. They both keep getting better and better over time (my opinion, anyway). The hops do fade a bit and the caramel does come up a bit but they are both incredibly smooth. The older one was done with the Budvar strain and while it always hinted of Budvar it now really tastes like the draught Budvar I drank in Europe as best I can remember. The "secret" is protection of oxygen, heat and light. Note that neither of these beers had a diacetyl or acetaldehyde problem. I don't raise temp at the completion of fermentation, in fact I drop it, but the beer does sit on the lees for a couple of weeks before I keg. This is not meant to be taken as advising against temperature increases. Commercial lager brewers use fermentation temperature profiles that involve high (by comparison to traditional lagering practices) temperatures precisely because acetaldehyde and diacetyl are reduced which allows them to shorten lagering time.