With the rise in popularity of mixed-fermentation beers, 100-percent Brett beers, spontaneously fermented beers and Lambics, wild ales, sour ales and farmhouse beers, the terms that define these beers get tossed around more and more. Some of these terms are used interchangeably, and some people interpret them differently, adding confusion. To help you better understand their similarities and differences, I’ll attempt to explain all of them below.
This vague and broad category of beers can be summarized as beers fermented with more than one yeast strain – usually a strain of Saccharomyces ale yeast along with some strain of Brettanomyces (aka Brett) yeast. These beers may or may not be fermented with bacteria (i.e., Lactobacillus and/or Pediococcus). Oftentimes, mixed-fermentation beers are fermented with ale yeast during primary fermentation followed by Brett in the secondary, or when barrel aging or refermenting in bottles.
100-percent Brett beers are fermented with only Brettanomyces yeast (i.e., no Saccharomyces yeast). These beers may be made with just one strain or multiple strains of Brett (e.g., bruxellensis, lambicus, claussenii).
As an aside, Brettanomyces is Latin for “British fungus.” It was first classified in 1904 when the cause of spoilage in British ales was being investigated.
SPONTANEOUSLY FERMENTED BEERS and LAMBICS
Spontaneously fermented beer is beer that has been naturally inoculated and fermented by wild yeast and bacteria in the air, rather than by pure or mixed cultures of yeast and/or bacteria. The most common way to make this beer is to pump the hot wort into a coolship, which is a wide, shallow and open tank, and allow it to cool overnight in the open air. This is when the wort is naturally inoculated by a mix of microorganisms (i.e., wild yeasts, including various strains of Saccharomyces and Brettanomyces, and bacteria, including Lactobacillus and Pediococcus – affectionately known as “bugs”) that happen to be floating around in the air. Usually, this method is only done in the cooler months, typically from late fall through early spring, when airborne microbes are most favorable.
Once cooled, the inoculated wort is usually pumped into oak barrels or foeders, where it picks up even more microorganisms residing in the wooden staves that were left behind from previous batches. This “straight” / “unblended” beer is often aged for months or years, and over time it will become funkier and more acidic.
Many U.S. breweries have begun making spontaneously fermented beers, including Russian River, Allagash, Jolly Pumpkin, Midnight Sun, Jester King, de Garde, and more.