Acetaldehyde in clean lagers

What yeast? Pitch rate? O2 at pitching?

 

My experience with acetaldehyde is limited to two instances, back when I bottled, and in both cases I attributed it taking the beer off the yeast too early and trying to drink the bottles early. Neither beers were true lagers. One was a pale ale made to resemble a pils, and the other was a hefeweizen. In both cases, I solved the problem by extending the bottle conditioning time a few weeks, at ~70 degrees. The yeast that were in the bottle cleaned up after themselves.

To me, it sounds like you might be moving your beer to the keg too soon, getting it off the main yeast mass before it has cleaned up. While there is some yeast in your keg, it is not as much as you left behind in your primary, and is further challenged by the low lagering temperature. Maybe keep it in primary until off flavors are undetectable over a several day period - I have moved my lagers to kegs in the 3rd or 4th week. Don't be afraid to do a longer D rest - there is more than just diacetyl to clean up, and at this stage, warmer temps are you friend. Finally, you might consider slowly reducing your temperatures to lagering temps over several days, so as not to stunt all yeast activity by shocking the yeast. I don't have tons of lager experience either, so I am speculating a bit, but I do think that rushing through the period when yeast still needs to be active is your problem here.

 

I agree with the ideas posted by pweis909, basically longer/slower is better. Also, I would get my hydrometer in on the act. IMO you want to start the d-rest before FG . . . maybe 3-5 points to go. I raise and lower my temps s-l-o-w-l-y, not positive this is important but that's what I would prefer if I were a yeast cell. If you search, you can get informed opinions that do not support what I just wrote above . . . but this is my method. So I recommend you aggressively go slow and take longer.

FTR; just starting my strike water for a lager this morning (Rauchbier) after having spent all day on a boat yesterday!

 

generally acetaldehyde is produced during the initial lag phase and growth phase of fermentation (which can take an upwards of 11 days) and is reduced during the maturation phase (which generally is days 12 - 21) YMMV as these are commercial rates which can be slightly faster than homebrew rates.

some factors that increase the amount of acetaldehyde initially produced during fermentation include

1. Rapid fermentation
2. Higher fermentation temperatures
3. Removal from yeast too early
4. Overpitching
5. Underpitching (just not enough healthy yeast at end of fermentation to reabsorb it)
6. Low aeration
7. Pressurized fermentation

some factors that increase the removal of acetaldehyde during the maturation phase include

1. Adequate yeast viability and vitality (Having enough healthy yeast that last through the maturation stage)
3. Warm maturation
4. Good initial wort aeration (leads to cell growth and yeast health)
5. Increased cell growth (produces more cells to reduce the acetaldehyde produced although it can increase higher alcohols and esters)

The interesting thing is that having lots of cell growth produces more acetaldehyde initially but also results in better clean up of the acetaldehyde produced.

 

Sorry please move #3 and #5 from the top list to the bottom list. I have to stop posting things early in the morning

 

I brew a lot of lagers and have never had acetaldehyde. Depending on the type of beer I age some longer then others. I pitch 2 vials of yeast and do not use pure oxygen. In the past I have even fermented at 66 degrees with no off flavors. Once primary is 75-80% done I move my fermenter to 65-66 degrees and leave there until 3 weeks of total fermentation. I then transfer to kegs. My technique may not be the same as others but it works for me.

 

You can also get acetaldehyde through oxidation of alcohol, so transfers should be as O2 free as you can manage.

 

Actually, #3 and #5 from the top list would only be moved down to the bottom list if the bottom list was things that decrease potential acetaldehyde clean up during the maturation phase. My early morning corrections are just as susceptible to error as my original early morning posts!