I brewed a gose about half a year ago. I intentionally soured the wort (not the mash) by adding a bottle of Cantillon geuze to it while it was still warm (around 50°C). Left it in a hot room (26°C) for 48 hours.
Stank of vomit like somethng crazy. Butyric acid, probably by geuze beasties combined with uncontrolled temperature and too much head space.
Still decided to boil since it didn't taste bad (or at least, not as bad as it smelled). Stank up the whole house, which didn't make the Missus none too happy and which has resulted in a perma-ban were brewing sour beer is concerned.
Post-boil, only a little of the vomit-smell remained (since most of it was now all over the house).
Fermented with top fermenting yeast (need to look up which one, not that you could tell in the end) which seemed to clear the remaining butyric acid smell just a bit.
The stench came back after a week or so in primary.
Racked to secondary, and despite being repeatedly and vociferously advice to dump the brew, I pitched a pack of Wyeast 5112 Brett brux, which I'd heard to be capable of metabolising organic acids to more savoury esters.
The beer's been sitting in secodandary for about half a year now, and the smell has made a winding journey from vomit, over pig sty, to sweaty parmesan, to something now resembling pine-apple scented band aids.
Flavour has evolved too, and is now incredibly complex and, well, weird. The salt and coriander of the original gose recipe, combined with the tartness coming from the Brett and the estery/phenolic metabolic by-products make for a beer unlike anything I've tasted before.
Also, almost all of the weat malt haze has disappeared, and the beer is now crystal clear.
While still not a beer I'd pour for just anyone, I think it has become interesting to a point of being presentable.
The kids call this one "dad's Puke Beer".
The Missus calls it "Get that thing away from me."
By which I mean to illustrate the power of Brett as a flavour modifier, and, in a pinch, a saviour of dodgy brews.
I think Chad Yakobsen and Michael "MadFermentationist" Tonsmeire are setting up casual experiments, trying to produce worts rich in "unwanted" precursors for Brett to turn into more desirable flavour compounds; my own limited experiences outlined above seem to corroborate there is merrit to the idea at least.