Changes

Reusing a sour yeast cake can often provide great results. Brewers have reported success repitching on very old yeast cakes (2 years) without getting off flavors from yeast autolysis. After several months, [[Saccharomyces]] tends to die off due to the low pH in a sour beer. The bacterias bacteria and [[Brettanomyces]] tend to survive the lower pH, and their cell counts can be high in even an old yeast cake. By pitching new wort on an old sour yeast cake, these microbes (particularly the [[Lactobacillus]]) have access to the simple sugars in the wort <ref>[http://www.themadfermentationist.com/2009/11/brewing-sour-beer-at-home.html Tonsmeire, Michael. The Mad Fermentationist. Brewing Sour Beer at Home. Last paragraph in the "Inoculation" section. Retrieved 2/19/2015.]</ref>. In general, washing the yeast cake is not necessary.

Some brewers have good success reusing a yeast cake or a portion of a yeast cake by leaving the wort in contact with the old yeast cake for 31-4 days. After 31-4 days, a fresh culture of Saccharomyces is pitched to finish the fermentation. The 31-4 day head start gives the souring bacterias bacteria a head start and results in a low pH beer. The harvested yeast cake can also be pitched at the same time as a fresh culture of Saccharomyces, or afterwards. The decided timing on when to pitch the harvest sour yeast cake will effect the outcome of the sour beer. Early pitching of the sour yeast cake generally produces a more acidic beer, and later pitching generally produces a less acidic beer.