Understanding the basics of sours means understanding Brettanomyces. I’ve seen multiple pronunciation descriptors, but generally hear breh-tah-no-MY-sees. This particular resilient yeast strain, Lauren Salazar said, is the bridge between beer and wine. (Brett can come out in certain wines, especially red, and at certain levels it gives a distinct taste that can be pleasing albeit acquired. But too much and it causes faces to squish and glasses to be pushed aside.)

via Beer 101: A look at Brettanomyces in sour beers | cleveland.com.