Sour beers are hugely popular with home- and commercial brewers alike. However, the term “sour beer” encompasses a large range of styles, methods, and flavors. In this talk, we’ll address variations in sour beers from sensory, microbiological, and stylistic perspectives. We’ll learn how we perceive different acids in beer, and we’ll examine the organisms that contribute to sourness, including some new research demonstrating that yeasts can contribute substantial amounts of acid. Finally, we’ll learn how homebrewers can use this information to influence the finished beer.