O2 tank questions....

My experience has been that high flow rates waste gas. The meter was hitting 20 ppm but as soon as the gas was turned off it fell right back to 10 or 12 or whatever. So the oxygen was being dumped, just not dissolving into the wort. Since we want dissolved oxygen and not just oxygen, a low flow rate allows for better absorption into the wort.

Note too that this was all informal. The DO meter was calibrated and dead nutz accurate but I wasn't measuring flow rate, didn't monitor temp (though the wort was below 70 ) and was really just futzing around with a fancy DO meter because I could. Even still, blasting the wort didn't help and wasted gas. I got better results moving the stone around in the wort with a low flow rate.
That's my observation.
Cheers.

 

Yes, anything that would reduce or eliminate the time the wort's surface area is open to atmosphere would increase O2 retention.

 

From a "gas dynamics" point of view the answer is "no". However, from an "absorption" point of view it's a definite "most likely".

There are a multitude of variables that control gas absorption . . . I understand maybe half of them. But once absorbed the gas will always move toward equilibrium. If you oxygenate to anything over 8ppm (normal oxygen level in water) it will start to diffuse out. If a 1/2 micron bubble of oxygen comes out of a stone, the wort will react to it regardless of flow rate. IMO it is a benefit to place the stone at the bottom of primary and constantly move it around so the bubbles are reaching as much of the wort as possible (absorption is more efficient when there is a greater differential of pressures). This is where an inline diffuser is superior as it basically interacts with all the wort.

All the bubbles you see at the surface are the ones that escaped absorption. But they remain at surface, at least initially. I think most brewers oxygenate, pitch, stir, seal . . . that takes all of a minute or two and little of the oxygen in the headspace escapes (my opinion here). Once sealed the little yeast buggers metabolize the absorbed O2 and as the level decreases the headspace oxygen will re-absorb into the wort (good for the yeast during lag phase). This happens if the headspace is air only, just a lower percentage of oxygen. Of course during active fermentation if any is left it will be mixed with CO2 and pumped out the airlock. This is why we leave our yeast starter flask covered but not sealed, we want air to interact with the starter wort. The goal here is yeast production (aerobic fermentation) rather than making beer (anaerobic).

For @riptorn a lot of theory here, from a practical point of view 1 or 1/2 l/min will definitely work and moving the stone during the process can not hurt. The math to accurately explain all of this is fairly overwhelming. In the past I've appealed to lurking Gas Dynamicists to jump into this discussion with no results . . . they must all be winos . . .

 

I may be under oxygenating my 5 gallon batches but I am still on my first red canister and I have used it for at least 10 batches. I pitch my yeast then put the wand in turn on the tank so I can barely see bubbles on the surface and then wave the wand around for 15-30 seconds. It has to be better than what I was doing before which was absolutely nothing.

 

Brewing next week, here's my class E in action:


New starter that hasn't started(yet) . . . all the bubbles are from oxygen that didn't cling to the wort as it rose to the top. But a couple of good shakes will help it absorb, plus any extra will mostly remain as a smorgasbord for the little guys.

Remember what I said about steel? All of those dark spots are rust (base is entirely rust). Gauge is in red band so it's hard to read, but it's probably good for another year or two. Then cut the end off, mount it to a swivel, fill with tacks and use as a cannon to repel boarders . . .