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10/09/09 08:49 PM  
Oxygen Permeability of a Brett Pellicle?
Does anybody know how permeable to oxygen a brett pellicle is? Just something I have been curious about. I imagine it is pretty high, but I have heard some claim that the pellicle protects the beer from oxygen, so I am curious how true that is.
10/10/09 04:33 PM  
Re: Oxygen Permeability of a Brett Pellicle?
I do know I have seen photographs in Wild Brews of partially open wooden vats/barrels and seeing a huge white mat of pellicle in there. I would bet that a hearty pellicle is fairly impervious to oxygen provided it is left intact during the lengthy secondary fermentation.

I for one cannot stand oxidation in any type of beer, so I rack my sours into a secondary while they are still fermenting a bit so the oxygen gets pushed out by the carbon dioxide scrubbing (unless its a lambic, which will stay in the primary).

10/11/09 04:14 AM  
Re: Oxygen Permeability of a Brett Pellicle?
One of the reasons yeast forms a pellicle is to regulate its oxygen intake. In theory, Brett should be able to pull the amount of oxygen that in wants through the pellicle as needed. Whether or not that amount of oxygen is ideal for a tasty beer fermentation is something I can't answer though. . .
Al B
10/15/09 02:39 PM  
Re: Oxygen Permeability of a Brett Pellicle?
Its never a clear-cut answer, many factors are involved. This depends nutrients available, temperature, and whether there is some CO2 being generated yet. Oxygen will passively enter the pellicle (depending on the container) where the cells at the bottom of the pellicle will utilize the O2 (along with available nutirents in the medium or beer). So in theory, it is minimal contact with the beer.

Hence over time the pellicle grows thicker.

However, if the brew is lacking starches/dextrins/amino acids, the O2 may have a detrimental effect long term, in the case of lambics, that effect could very well be vinegar.

10/15/09 04:44 PM  
Re: Oxygen Permeability of a Brett Pellicle?
So would it be safe to say, Al, that if your airlock goes dry in the first few months the effect is likely not very damaging? And if this happens late in the cycle of fermentation then it is much more likely to result in either oxidized beer or severely acetic beer?

Lets use the example of a carboy, where presumably the only oxygen entering solution would have to be through the pellicle.

10/15/09 07:39 PM  
Re: Oxygen Permeability of a Brett Pellicle?
Wouldn't that long term effect also include a pretty heavy oxidation as well? How long did it take for the pellicle to form?
Al B
10/16/09 06:42 PM  
Re: Oxygen Permeability of a Brett Pellicle?
I've never had an oxidized sour brew, although when an air lock went dry after a while, I did get vinegar.

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Around Bruges in 80 Beers: 2nd Edition

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