Changes

Reusing a sour yeast cake can often provide great results. Brewers have reported success re-pitching 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 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 will harvest a certain amount of trub from their fermenters (500ml 500mL for example), and use only this amount to inoculate a new batch of beer. This will allow the brewer to control the amount of dead trub material that goes into the fresh new beer. Michael Tonsmeire often advises that the brewer also pitch a fresh culture of Saccharomyces <ref>[http://www.themadfermentationist.com/2009/11/brewing-sour-beer-at-home.html Tonsmeire, Michael. The Mad Fermentationist. Brewing Sour Beer at Home. Comments section. Retrieved 2/19/2015.]</ref>.

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 1-4 days. After 1-4 days, a fresh culture of ''Saccharomyces'' is pitched to finish the fermentation. The 1-4 day head start gives the souring 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 acidity of the sour beer. Early : early pitching of the sour yeast cake generally produces a more acidic beer, and later pitching generally produces a less acidic beer.

As with all methods, the species and strains of the microbes being used should always be taken into consideration. Experimentation and repeated processes should be carefully employed by the brewer in order to find the best results for their cultures. For example, using different strains of ''Saccharomyces cerevisiae'' as the primary fermenter can could produce widely different results, and the use of 10-30 IBU's in the wort can be used to inhibit the lactic acid bacteria if they become too strong and produce too much acidity.