haltz wrote:Given that most beer isn't aged for that long, even in humid conditions (which you don't want unless they specifically help brett fermentation) you aren't going to see an appreciable change in abv.
We're not talking most beer though, we're talking specifically about brett, lacto, other long-aged beers that are kept typically in barrel rooms where there is some control over the humidity. These yeast bugs eat up stuff that other yeast doesn't always get to, creating more alcohol by volume in the tank/barrel, which then, under controlled humidity, evaporates out.
Look at Berliner Weisse beers. They age for a looooooooong time. And come in at 2.8-3.5% ABV. They get an extended, cool aging in low humidity. The alcohol, which can't form the bonds water can, evaporates out.
You can scan the
BJCP Guide on sours and find a lot of low-alcohol beers, medium tops. Once in a while they'll hit 7-8% but it's rare. The long, controlled fermentation causes alcohol to escape the wort as it ferments.
In a nanobrewery that's cranking out DIPA after DIPA, sure, they'll ferment hot and fast, get rid of more alcohol than water by design, and crank out 9% DIPAs.