How much oxygen

[Crackin]

Using a oxygen wand / bottle, without a flow meter, how much is necessary for a medium gravity lager? I have been getting too much acetaldehyde out of 2206 yeast that takes forever to go away. Right now I have been bubbling O2 for 90 seconds, just so that the O2 breaks the surface with the stone at the bottom of the carboy. Actually, when I move the stone around, the O2 is all absorbed before it breaks the surface, so not much foaming.

What is everyone else doing, without a flow meter?

[ajdelange]

What you are doing with the O2 seems about right. Perhaps you might want to increase the time to 2 min or 2 1/2 but I don't think that's going to solve your acetaldehyde problem. First off, let's make sure you are really talking about acetaldehyde. I have recently experienced two beers with really strong acetaldehyde and in the one case was told the beer had a diacetyl problem. I have also seen questions posted about acetaldehyde where the problem was diacetyl so there seems to be some confusion about this. Acetaldehyde, at permissable levels tastes and smells like apples. Think Budweiser. At stronger levels it begins, unsurprisingly enough, to smell aldehydic i.e. somewhat like formaldehyde but still fruity. Diacetyl, OTOH, smells buttery at medium levels. It's the stuff you used to smell when you went into a movie theater (but no more).

If you have acetaldehyde at the aldehydic level the problem is probably Zymomonas infection - not a problem with the yeast. All yeast produce it: sugar --> pyruvic acid --> acetaldehyde --> ethanol. It is the step in which pyruvic acid gets converted to acetaldehyde in which the CO2 is released but more important is to realize that where there is alcoholic fermentation there will be some acetaldehyde. The yeast eventually clean it up. Zymomonas does not.

[Crackin]

I have had this off-flavor in all my lagers so far, on two separate runs; this spring and this fall. This spring, all 4 lagers I did had a fruity flavor that eventually dissapeared over 3 months lagering time. This fall, new pitch of yeast, same strain, 2206, and same flavor. Because the off-flavor went away, I suspect it was acetaldehyde. I just brewed a dunkel tonight, off a repitch, and pitched extra yeast and gave it 2 minutes of oxygen. We shall see if that helps. I doubt that previously I have over pitched or over oxegenated, so that is the path I am taking. I will post in a month or two on the results.

Doug

[ajdelange]

Sounds like the classic acetaldehyde profile. Also sounds as if what happened during lagering is what is supposed to happen during lagering. I'm guessing you will be OK. IOW if it went away during lagering it was not from infection.

[jwatkins56550]

You could try a diacetyl rest to speed up the reduction process.