Klickitat Jim wrote:This is my thinking too. Seems like I've read or heard Chris White, or someone, say that it takes about 3 or 4 hrs and they are done with O2 uptake. If I added a second dose it would be at about 4 hrs in. But in my opinion if you pitch a healthy fresh starter of appropriate size and cell count, adding a second dose is not, or less, necessary. Why do we prefer stirplates? Because they continue to add O2 and therefore grow more cells. So if you pitch enough healthy cells to your beer why do you need to grow an extra amount of cells?
I know a lot of folks add O2 at 24hrs and get good results. I'm not disputing anyone's experience. I'm just saying that our basic brewing principles seem to indicate its not necessary. My last big beer was a 1.082 Quad that had 14 lbs continental pils, a pound of special B, a pound of dark candy syrup, and a pound of cane. I used the sugar in the boil, not added later, and only one dose of O2. With a proper pitch of Trapist yeast it got down to 1.008 in 21 days. Not infected so thats not what got me the low FG?
Having said that, I think if you add O2 a day or 2 or even 4 later that the yeast will clean it up. Im just not convinced that its really improving the beer all that much.
You really can't measure it in time. Every situation is going to be different. The reason we need to grow cells with a healthy pitch is because even a healthy pitch is not the amount of cells needed to ferment the beer. Think of it like that expanding insulation foam you use when you put in a new window. There is a correct amount to put in there - too little & it won't expand to fill the void, too much & you're the contractor that my last landlord constantly hired (ok, sloppy, but I would never assume anyone is as big of an idiot as that guy). You want that healthy pitch that's going to grow into the perfect amount.
The yeast is going to grow with or without the O2. It's the new cells that we're concerned about. A healthy pitch (in regards to nutrients & O2, not size) is going to produce healthy cells. If you deprive them of that O2 or nutrient, you get mutants, early flocers, late flocers & that yeast cell that just sits there & licks the side of the carboy.
In the case of O2, I simplify the yeast's cycle in 2 major parts - aerobic & anaerobic. In the first cycle, they're sucking up that O2, making buddies & preparing for battle. In that 2nd cycle, they're not taking up the O2 anymore or making buddies, they're too busy... the war has begun. Now if that first cycle takes 3-4 hours or 12 hours, it doesn't matter all that much but it's safe to keep supplying them... but once that first bubble of CO2 appears, the war is on. No more O2 after that. Even if they clean it up later (which I'm not so certain of), it's still in the beer when it shouldn't be.
Cliffs notes: No fermentation, add some O2. Fermentation, do not add any more O2.
BN Army // 13th Mountain Division 
