I've read that pure b. bruxellensis is supposed to add a spicy, funky flavor to beers. To test this out and get ready to brew an all-brett beer, in the last couple weeks I bought a vial of WL650 -- Brett Brux, and pitched to a small, 1 gal. batch of beer, just to see what it would do (and, in the process, build up the tiny amount of yeast in the vial to a more pitchable rate).
Well, several weeks on, the beer fermented, formed a pellicle, the pellicle collapsed, and it went inactive. Once it finished bubbling for good, I decided it was time to give it a taste -- and it is SOUR. Its flavor is good, not unlike an Oud Bruin, but not at all what I expected from my research.
So, here's the question: did it go sour because of some overlooked characteristic of b. brux, or did it get infected somehow? As a perhaps important aside, the sourness is not the mouth-puckering sourness of vinegar. To me it tastes more lactic, like yogurt.