Common misconception, Brett. is not sour. It is bacteria that makes the beer sour, i.e. Lacto and Pedio. Brett. does however do well in a sour environment (pH=4.5). Brett. is more barnyard and funk.
does make it sour. The by-products of fermentation contain a number of organic acids, including acetic.
I am not an organic chemist or microbiologist, but I do play one on the forum
. I do have a medical degree so microbiology is not foreign to me and I understand the concepts. I don't claim to know a lot of the science, but I understand it.
I will not argue that in normal or Brett. metabolism that acids are release. Yes, it is true that Brett. produces acetic acid and other organic acids a by-product of fermentation. But, it is at or below the flavor threshold. Brett. actually quits working below a pH of 4.0 to 3.8 or so. Beer in an of itself in its very nature is acidic. NORMAL yeast metabolism produces organic acids such as acetic, lactic, butyric, caproic, decanoic, succinic, and, octonoic acids. Most beers after fermentation have a pH in the 4.5-4.8, or acidic. I have an all Brett fermented beer in the 4.3 pH range, the same base beer produced with WLP007 is in the range of 4.4. Fairly close. So based on your above statement, regular brewer's yeast makes beer sour. As with Brett., most of these acids are produced at or below our taste thresholds. The main souring organisms in sour beers are bacteria: lacto, pedio, and acetobactor. These organisms DO bring the pH down below 3.8 and create organic acids that surpass our flavor threshold. This is why Brett is added prior to the souring organisms innoculation. Once the pH drops below 4.0 the Brett. stops working. So, while I won't dispute that Brett. and all brewing organisms produce acids...in terms of flavor acidic does not necessarily equate to sour.