ercousin wrote:JasonTremblay wrote:You can't realistically over-aerate with air
You also can't aerate enough with only air, theoretically. For something high OG you want much more than the 8 ppm max you get with air, closer to 12-16 ppm would be better, which needs pure O2. A 2nd aeration after 12-18 hours would help mitigate this of course. I think a carb stone, filter, regulator, and CDN Tire O2 tank is a much simpler setup than having to plug in an aquarium pump.
O2 wands tend to be designed with carboys in mind though, so aerating into a keg with one could be a pain.
I don't ferment in carboys anymore
So, I did some poking around and hauled out my copy of
Yeast from White and Zainasheff. In general, yeast does best with atmospheric levels of O2 (going above this tends to slow down the yeast). In the specific case of high gravity beers:
If it is a very high-gravity wort, more than 1.092, you must aerate with pure oxygen, as air will not provide a high enough level of dissolved oxygen.
Unfortunately, that still might not be enough for beers higher than 1.083. For high-gravity beers, adding a second dose of oxygen between 12 and 18 hours can help fermentation speed and attenuation ... Research also indicates the addition of oxygen (some say more than 7 ppm,, some say more than 12 ppm), at 12 hours increases the fermentation speed by 33 percent and decreases flavor compounds ... Why wait until 12 hours? You are waiting for the yeast to complete at least one cell division.
They also recommend rather large pitching rates and, after 48 hours, fermenting at 25C to keep the yeast at their most active.
IME, neither one of us scores a knockout. But the important bit, I think, is to aerate your wort since vigorous splashing for 5 minutes is less than 3ppm of oxygen, much less than the 7 or 8 you want with regular strength wort. Unless you go with dry yeast.
FWIW, the O2 wand you pictured is virtually identical to my system for aerating in a keg (down to the sterile air filter). The big difference is that I'll aerate for a half hour or more and don't bother with the stone.
