My question is it possible to over oxygenate a yeast starter? I started brewing 10 gallon batches, I only have one stir plate and I'm using two different yeast strains. So one is on my stir plate the other is just a simple starter. So can I occasionally inject pure O2 into the simple starter without ill effects? And if so how often? I injected the simple starter with O2 prior to pitching the yeast as well. Thanks for the help!
Over oxygenation?
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Yes, I think it is possible. While not so much when using a single dose for fermentation. I think repeated doses to a starter may lead to trouble. I clipped this from another homebrew forum:
"When oxygenating starters, you cannot use pure O2... the reason is that the uptake occurs too fast and without a dissolved O2 meter ($$$), you cannot tell when to stop. The way to properly do this one is to aerate using a high pressure aquarium pump, sterile air filter and a stainless steel aeration stone, all of which are readily available. It is virtually impossible to over-aerate using air, so you will avoid oxygen toxicity problems that will occur if trying to do this with pure oxygen." (Eric Watson; BeerTools.com)"
It would certainly be nice to somehow treat both strains the same as the one you have on the stir plate will achieve a higher cell count and may dominate the fermentation. My first thought was to alternate the starters on the stir plate but I think you would experience foaming issues after allowing one to sit. Perhaps by starting slow and gradually increasing the speed you could avoid foam over.
I think that's a good method if you don't have a stir plate. Perhaps it would be safe to give it a couple more doses of 02, say one after 6-8 hours then another an hour or so before you think it will finish. If I tried it, I would keep it to a short burst of maybe 5 seconds.
As you know, stir plates are the best for starters. If ran at a high speed, the spinning action will remove the CO2 and bring in small amounts of O2. A small but consistent supply of O2 will do wonders for yeast health and keep the yeast in reproduction mode, win, win.
Even with pure O2 you would have a tough time over oxygenating your beer wort. Any excess O2 is going to get scrubbed during fermentation by all of the CO2 gas percolating through the beer.
Here's Wyeast's take on it: Oxygenation of wort
Here's Wyeast's take on it: Oxygenation of wort
Great info. I think I'm going to give the starter a small bursts of O2 in a couple hours.
