Does overpitching reduce attenuation?

[Crackin]

I brewed a Dunkel, o.g. 1.054 and it finished 3 weeks later at 1.020.(62% AA). I purposefully overpitched as an experiment because of some acetaldahyde issues I have been having. I re-picthed 500 ml of non-separated slurry from a previous batch, which is about twice the suggested amount. Can overpitching reduce attenuation like that?

Doug

[BigNastyBrew]

I purposefully overpitched as an experiment because of some acetaldahyde issues I have been having.

Could be wrong here but doesn't overpitching CAUSE acetaldehyde? Yeast run out of food in competition with each other? Thought I heard or read that.

[Crackin]

I believe you are correct. This was just an experiment, because with the 6 previous lagers, I have had acetaldahyde, and I thought I was pitching the correct amount. That means, if anything, I was underpitching. The other factor is O2, so I added extra O2 this time too. Just curious about the attenuation, thing, though.

[BigNastyBrew]

Not sure if it helps you much but I've been doing a few lagers over the last few months and I have found that what I prefer is to use more yeast vials and smaller starter to get the right pitch rate versus big starter and less vials. It appears as though I get a cleaner fermentation and better attenuation that way.

[Crackin]

What about re-pitching? Or do you start with fresh yeast everytime?

[BigNastyBrew]

The short of it: I use fresh yeast every time.

I do not re-pitch, yet. Not because I don't ever want to but more because I haven't learned that yet. I jumped into this hobby head first and have learned so much this year. I started with Mr. Beer on Christmas of last year. I placed re-pitching further down on the to-do list, if you will.

[dunleav1]

I've had better attenuating beers when repitching especially lagers.
I like the 3rd and 4th generation the best.
I always pitch 150ml more than the mymalty calculator.

[brewinhard]

Have you other lagers/beers underattenuated as well? Have you checked your thermometer's calibration lately? 1020 may sound high and look high, but if you carb that sucker up to 2-3 volumes, you won't even be able to tell the difference if it had finished at a 1015 or so. This I know from experience with my last pumpkin spice ale that finished at a 1020 and tastes delicious (even though I was shooting for a 1015)!