What is typically the main ingredient in sour beers that contributes to their unique flavor?

Sour beers are characterized by their tart and tangy flavors, which primarily come from the presence of lactic acid produced during fermentation. Lactobacillus is a type of bacteria that plays a critical role in this process. Unlike traditional beer fermentation that primarily relies on yeast to convert sugars into alcohol, sour beers often incorporate Lactobacillus to create that distinct sourness.

In brewing sour beers, Lactobacillus can be introduced intentionally, either through specific souring techniques or by allowing spontaneous fermentation in conditions that allow wild yeast and bacteria to thrive. The lactic acid produced by Lactobacillus is what notably contributes to the sour flavor profile.

While yeast is indeed essential for fermentation in all types of beer, including sour varieties, it is not the primary contributor to the sour flavor itself. Hops are generally used for bitterness and aroma rather than sourness, and caramel malts, which can add sweetness and color, do not play a role in producing the sour characteristics that define these beers. Therefore, the main ingredient contributing to the unique flavor of sour beers is Lactobacillus.