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Yeast contamination is a concern when storing soured wort, especially in a sealed vessel such as a keg. Pure cultures of ''Lactobacillus'' cannot effectively ferment most sugars in wort (see [[Lactobacillus#100.25_Lactobacillus_Fermentation|100% ''Lactobacillus'' fermentation]]), therefore there are a lot of sugars available for contaminants to take advantage of when storing wort that has been soured but not fully fermented with yeast. Good sanitation practices are of the utmost importance. Equipment used should be thoroughly clean and ideally sterilized, or at least boiled if possible. If a yeast contamination goes unnoticed, then the keg can become heavily pressurized and potentially dangerous even when stored cold. We recommend regularly checking a keg of soured wort to ensure that over-pressurization does not occur, or use a spunding valve to ensure that over-pressurization does not occur.
These methods only work with pure cultures of ''Lactobacillus'' (or at least cultures that do not contain an unwanted microbe that can take advantage of the residual sugars in the soured wort, such as yeast). Cultures from grains, [[Mixed_Cultures|mixed cultures]], or cultures from other fermented foods such as those listed on the [[Alternative Bacteria Sources]] wiki page, should be treated as a mixed culturethat potentially contains yeast. See [[Mixed_Fermentation#Storing_a_Yeast_Cake_or_Sample|Storing a yeast cake or sample of a mixed culture]].
==Contamination Concerns==