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→Refermentation
===Refermentation===
Whenever fruit is added to a beer that hasn't been pasteurized, a re-fermentation will occur because new sugars from the fruit are introduced to the microbes that are still alive in the beer. This re-fermentation can take some time to being, and some time to finish, depending on the beer. In general, the fruit should be allowed to finish fermenting before packaging. An alternative method is to ferment the fruit more quickly in a separate fermentation tank with ''S. cerevisiae'' and then blend the fermented fruit into the beer; see [[Soured_Fruit_Beer#Other_Alternative_Processing_and_Fermentation_Methods|Other Alternative Processing and Fermentation Methods]] for more information. For information about packaging beer with unfermented fruit/puree/juice, see [[Unfermented Fruit Beer]].
Regular beers and kettle sour beers often contain living ''S cerevisiae'' as long as they are not aged for too long (less than a month). [[Mixed Fermentation]] sour beers where ''Brettanomyces'' was pitched will most likely still contain living ''Brettanomyces'' cells even after a year or two of aging. In the case of ''Brettanomyces'', only a small population of surviving cells is enough to kick off a re-fermentation. For beers that have aged for a very long time in very sour conditions, fresh ''Brettanomyces'' or wine yeast can be pitched to ensure re-fermentation of the fruit.