General Category > Yeast and Fermentation

Oxidation during fermentation

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edward:

My question is this.  How long can you keep a beer in a plastic fermenter before oxidation becomes an issue?  I've left an RIS in the primary(plastic) for a month before, but then again a little oxidation seems somewhat common on those styles after you age them.

3 weeks?  4 weeks?  5 weeks?  I always hear about oxidation in plastic buckets but I never hear about how long it actually takes to develop.

My next batch of pils I may do a side by side comparison using a 2 week primary in plastic for both and then a 3-4 week lager in a glass carboy and plastic bucket.

If its already been done please let me know the results.

bluesman:
Oxygen will eventually find it's way int the beer if given enough time. It will permeate through the walls of the fermenter and the seal of the lid. How long? That's a good question but I think it starts to happen almost immediately to a very small degree. However alot of that is offset by the production of CO2 during the fermentation. I have fermented some big beers in the primary for upwards of 4 weeks without detriment to the beer but I would suggest minimizing the beers exposure to the fermenter. When the beer has finished fermenting it should be removed from the bucket.

edward:
IMO oxidation doesn't really start penetrating into the plastic primary until fermentation starts winding down.  So perhaps 4 to 10 days depending on the beer. 

I'm really hoping to find out timing wise that at what point keeping the beer in the primary becomes noticably oxidized.

Kaiser:
I don't think the production of CO2 drives out most of the CO2 during fermentation. It's the yeast that is consuming it. The rate at which any gas permeates during a membrane is determined by the gas concentration (to be precise partial pressure) on either side of the barrier and the barriers permeability for that gas. You could have 100 psi CO2 on the other side but the O2 diffusion into the vessel is not affected. At least that is my understanding of the mechanisms involved here.

So you should move the beer once fermentation is complete. But don't rush it too much. Let the yeast truly finish the beer and the little O2 that the beer will pick up likely helps its aging process since stong dark beers seem to benefit from a little oxidation, IMO.

Kai

edward:

--- Quote from: Kaiser on January 20, 2011, 11:33:44 AM ---I don't think the production of CO2 drives out most of the CO2 during fermentation. It's the yeast that is consuming it. The rate at which any gas permeates during a membrane is determined by the gas concentration (to be precise partial pressure) on either side of the barrier and the barriers permeability for that gas. You could have 100 psi CO2 on the other side but the O2 diffusion into the vessel is not affected. At least that is my understanding of the mechanisms involved here.

So you should move the beer once fermentation is complete. But don't rush it too much. Let the yeast truly finish the beer and the little O2 that the beer will pick up likely helps its aging process since stong dark beers seem to benefit from a little oxidation, IMO.

Kai

--- End quote ---

The solubility of oxygen would be affected by the partial pressure of the gases/liquids inside the fermenter.  But you're correct that diffusion of air through the plastic would be occurring from the beginning.

If oxidation from air is the big concern couldn't you just immerse the whole fermenter in a water bath?  Then the diffusion would be much lower (or nil) since the solubility of oxygen in fresh water is 9 ppm at 20 C.

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