Kettle sour

In the kettle sour method, lactic acid bacteria are added to the wort before boiling and it is soured for several hours to days. It is then boiled, which kills the bacteria, and the beer is fermented with regular yeast.

This produces acidity in a short time and with little contamination risk for the brewery. The method is often used for gose, Berliner Weisse and modern fruited sours. Traditional sour beers, by contrast, often mature for months with mixed cultures.