Oxygen at start of fermentation, pressure fermenting and you.

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Elric

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When pressure fermenting has anyone ever thought to start under pressure with O2 or regular air to give that extra O2 for the initial lag phase for the yeast? I figure it's a win/win. You can start pressurized without having to waste bottled co2 and you are giving some extra oxygen for the initial yeast build up. Thoughts? Comments?
 

DuncB

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Well I've been pressure fermenting a while, but just started supplementary oxygen.
From my readings too much oxygen can be a bad thing as in high doses it's toxic to yeast. Strangely to humans as well.
I follow the guidelines of using the 0.5 micron aeration stone for about 1 minute at 1 litre per minute ( in reality flows a bit more than this) in the fermentasaurus and then pitch yeast and close lid. So there is a bit of extra oxygen in the headspace, I also " fill " the collecting bulb with oxygen and then attach that and then open the valve which releases that bubble of oxygen up through the wort, mixes it more and is also in the headspace as a supplement. The ferment was crazy with this last week and I also used the oxygen on a wine kit and that finished ferment in 9 days instead of 14 previously at the same temp and a little lower Final gravity.
Regarding wasting CO2, oxygen is more expensive so not sure logic there.
You could pump air into your sealed fermenter, that would raise the partial pressure so theoretically make more available for the yeast , but you'd have to have the pressure pretty high. I suppose about 5 atmospheres to get the partial pressure of oxygen as high as 100% ( not really achievable ) and then the pressure would probably be inhibitory to the yeast growth.

You are going to make loads of CO2 to use for purging kegs with your ferment etc so you'll save that way. Could even run your kegerator for a day or so off the excess gas ( if you have an inline filter ).
 

day_trippr

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What readings?
Unless I'm mistaken, Chris White in Yeast noted a fermentation started with 40ppm O2 concentration had no detectable defects...

Cheers!
 

heartofgold

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Keep in mind that pressurization itself is not the goal of pressure fermenting. The goal of pressure fermentation is to control ester and fusel alcohol production through the metabolic suppression of the yeast from high CO2 concentrations. In that sense, high pressure with O2 is counter-productive, especially during the lag phase when the yeast are just getting started.

You are better off helping the yeast build their sterol reserves with dissolved O2 in the wort, and at regular pressure, via bubbling O2 (or air) into the wort. at the beginning of the fermentation. O2 in the wort can cause staling reactions, so you want it out of your fermentation as soon as possible! The yeast helps here and will consume O2 in the wort quickly (in minutes! 20 - 120 mins depending on temp). O2 in the headspace is relatively inaccessible due to the slow gas exchange that happens at the surface of your wort. So yes, O2 pressure can increase that a bit, but not at the rate that you were hoping for.

For pressure fermentation, let the CO2 from the yeast create the pressure. There's no need to waste bottled CO2 for this purpose. Indeed, I use the volumes of extra CO2 created from my pressurized fermentations to purge my corny kegs ... the best CO2 you can get!
 
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Elric

Elric

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Thanks guys! I figured there was a reason people weren’t doing it. Your comments make a lot of sense. I currently pressure ferment with the same process you describe @heartofgold and have been happy with it.
 

Dr_Jeff

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I ferment under pressure and have for 5+ years now.

As to oxygen, I run oxygen in line on all of the wort from the cfc to the fermenter, it is basically foam when it hits the fermenter with great results. Sometimes the yeast is already in the fermenter other times, I add the yeast after the wort. What I "think" works best is after it comes to a boil, add a pint or so to the fermenter(stainless steel), give it 10-15 minutes to cool, add in the yeast, then when the chilling is done, add the wort and seal up the fermenter. It's usually going strong shortly.
 

Unicorn_Platypus

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When conducting a pressurized fermentation after pitching does it make sense to purge the headspace with CO2 prior to sealing it off with a spunding valve?

Under a normal non-pressurized fermentation the CO2 produced would naturally flush out the air in the headspace

However if sealing it off at the start of fermentation wouldn't there be O2 left in the headspace that the yeast wouldn't neccesary consume?
 

DuncB

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Any oxygen in the headspace will either get used by the yeast or flushed out by the many litres of CO2 produced. I do sometimes check that the fermenter seal is ok under pressure, I have had it where the valve wasn't seated properly on the fermentasaurus and once the active CO2 production has finished find that it was masking the leak and discover the fermenter with very little or no psi in it.
But that CO2 is added supplementary to the oxygen already added.
 
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