The St. James Gate Brewery in Dublin produces a beer called Guinness--you might have heard of it. Actually, it produces a whole bunch of beers, and they're all called Guinness. They vary from the light-bodied draft beer you get in pubs to a strong Nigerian version that employs sorghum rather than barley. My favorite--and one of the best beers in the world--is the strong version you can find in bottles with the name "extra stout." What makes it delightful are not the virtues of density and creaminess (though virtues they are), but a characteristic sour tang.
Jackson attributes this to funk resident in the crevices of the 100-year-old wooden tanks at St. James Gate in which only the strong stuff ages. Diageo, the parent conglomerate, denies this, but something's causing it. Rumor (and Jackson) credit a certain strain of yeast known as Brettanomyces. In the brewing world, Brett cultures have notorious reputation and are mainly regarded as contaminants. So profound is Brettanomyces (the cool kids call it "Brett") that brewers regard porous equipment (plastic, rubber, cork, wood) as permanently defiled and useable only in beers where Brett character is tolerated. On the other hand, Orval, the extraordinary lambics, Belgian browns and reds and others include it in their world-reknowned recipes. So you can't throw the Brett out with the bathwater.
I have decided to test the theory. I am in the midst of brewing up a batch of Irish stout, a fairly standard recipe that employs roasted barley, as appropriate to style. But after an initial fermentation with a standard ale yeast (I eschewed an Irish strain, rogue that I am), I'm going to dump in a Brett culture to finish it off. Brettanomyces are apparently voracious eaters and can gobble down sugars regular Saccharomyces (ale yeast) can't digest. Brettanomyces--the goats of the yeast world. My intention is to give the beer a wee taste of the sour without overwhelming it. We shall see.
In any case, I will report back as the experiment evolves. I don't know that I can prove what lives in the vats at St. James Gate, but you never know. I may also prove what doesn't live there. Stay tuned.