Brett beer fermentation

[Cody]

Which can be desirable traits in some styles, not an unfortunate side effect. Flander's Red for example, would not be the same style without a touch of that acetic quality requiring oxygen

You're right, it wouldn't be a Flander's Red without the oxygen...it would be a Flander's Brown.

[BrewerJ]

That was my whole point. There is acetic acid being created simply because it's in the barrel. The organisms producing the acetic acid only do so in the presence of oxygen, which the barrel is letting in. If you were to split identical wort between a closed stainless vessel & a barrel, the barrel will always sour faster from the acetic acid production that's going to be stifled in the stainless system that is preventing the oxygen from contacting the beer. And it's not necessarily souring more quickly as much as the acids being produced are more harsh, which creates an up-front, aggressive perception of sourness - the difference between how sour something tastes versus it's actual measured pH. All barrel fermented/refermented beers will have some level of acetic acid present, however with many beers it's not as evident since another culture already has taken over the beer limiting how much acetic acid is able to be formed. I believe the pitch-lined barrels also slow down the rate & amount of oxygen that's being let in, but I could be wrong on that particular point.
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I agree on your assesment of stainless fermentation oxygen free vs barrel aged with oxygen. I also agree with acetic acid being produced that is undedetectable. However I am comparing three month or less fermentation times carboy with silicon stopper vs barrel. Both of these have almost identicle oxygen permeability rates. About 20 02cc/L/year. For the first month or two the beer is still off gassing and fermenting. Positive pressure pushing out any oxygen. I dont think there is much if any acetic acid production in that short of time with little to no oxygen. The beer in the barrel will always be more sour and its not due to oxygen level. Since the carboy recieves the same amount. I say its the magic of the wood.

[brewinhard]

That was my whole point. There is acetic acid being created simply because it's in the barrel. The organisms producing the acetic acid only do so in the presence of oxygen, which the barrel is letting in. If you were to split identical wort between a closed stainless vessel & a barrel, the barrel will always sour faster from the acetic acid production that's going to be stifled in the stainless system that is preventing the oxygen from contacting the beer. And it's not necessarily souring more quickly as much as the acids being produced are more harsh, which creates an up-front, aggressive perception of sourness - the difference between how sour something tastes versus it's actual measured pH. All barrel fermented/refermented beers will have some level of acetic acid present, however with many beers it's not as evident since another culture already has taken over the beer limiting how much acetic acid is able to be formed. I believe the pitch-lined barrels also slow down the rate & amount of oxygen that's being let in, but I could be wrong on that particular point.
.

I agree on your assesment of stainless fermentation oxygen free vs barrel aged with oxygen. I also agree with acetic acid being produced that is undedetectable. However I am comparing three month or less fermentation times carboy with silicon stopper vs barrel. Both of these have almost identicle oxygen permeability rates. About 20 02cc/L/year. For the first month or two the beer is still off gassing and fermenting. Positive pressure pushing out any oxygen. I dont think there is much if any acetic acid production in that short of time with little to no oxygen. The beer in the barrel will always be more sour and its not due to oxygen level. Since the carboy recieves the same amount. I say its the magic of the wood.

It could possibly be that the surface area of the larger barrel actually houses denser populations of bacteria and brett that are residents vs pitching in a carboy.