Before the advent of refrigeration and advances in the science of fermentation in the mid-nineteenth century, almost all beer was, to varying degrees, sour. The culprits were pre-modern sanitation and poorly understood, often naturally occurring bacteria including Lactobacillus and Pediococcus, as well as Brettanomyces yeasts, which can contribute a hint of tartness and characteristic “funky” flavors and aromas, sometimes compared to leather, smoke, and “horse blanket.”