Sour beer is a unique style of beer that is brewed using a process called mixed fermentation. This means that instead of relying solely on brewer’s yeast to ferment the wort, sour beers incorporate a diverse array of microorganisms, including bacteria and wild yeast strains like brettanomyces.
There are a few different methods for brewing sour beers, but they all revolve around the concept of introducing these wild microbes into the brewing process. One common method is spontaneous fermentation, where the wort is exposed to the open air to allow the natural yeast and bacteria present in the environment to inoculate the beer. This method is often used in traditional Belgian lambic and gueuze production.
During spontaneous fermentation, the wort is typically cooled in large shallow vessels called coolships, which allow for maximum exposure to the air. As the wort cools, it attracts airborne microbes that begin to ferment the sugars in the wort. This process can take several hours or even days, depending on the desired level of sourness and complexity.
Another method for brewing sour beers is known as inoculated fermentation. In this approach, brewer’s yeast, brettanomyces, and bacteria are intentionally added to the wort together. This can be done by pitching a blend of different yeast and bacteria strains, or by adding a mixed culture of microbes obtained from a previous batch of sour beer.
Once the wort and microbes are combined, the fermentation process begins. The brewer’s yeast and brettanomyces will consume the majority of the sugars in the wort, producing alcohol and various flavor compounds along the way. The bacteria, on the other hand, contribute to the sourness of the beer by producing lactic acid.
The fermentation process for sour beers is typically much longer than for other beer styles. While a standard ale or lager may ferment in a matter of days or weeks, sour beers often require months or even years to fully develop their complex flavors. This extended aging period allows the wild yeast and bacteria to slowly work their magic, creating the unique tart and funky characteristics associated with sour beers.
Throughout the aging process, the beer may go through additional transformations as the microbes continue to interact with the remaining sugars and compounds in the beer. This can result in a wide range of flavors and aromas, including fruity, funky, and even barnyard-like qualities.
Once the desired level of sourness and complexity is achieved, the beer can be packaged and enjoyed. Some sour beers are bottle-conditioned, meaning that a small amount of sugar or additional yeast is added to the bottle to facilitate a secondary fermentation. This can result in natural carbonation and further development of flavors over time.
Sour beers are brewed through mixed fermentation, whether it be through spontaneous fermentation or inoculated fermentation. The process involves introducing wild yeast and bacteria into the brewing process, allowing for an extended aging period to develop the unique tart and funky characteristics. The result is a complex and often sought-after style of beer that appeals to those with a taste for the unexpected.