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'''Wort Souring''' (formally "sour worting") is a process in which lactic acid bacteria (usually ''[[Lactobacillus]]'' , although there are also [[Pediococcus]] cultures available that work well for this technique) is given a "head start", pitched before the yeast so that it will be able to produce significant amounts of lactic acid before the ''Saccharomyces'' completes the main fermentation. There are several variations on souring wort, including souring in the primary fermenter, souring in a secondary vessel, or even souring in the boil kettle itself. There are also various methods of inoculating the wort with ''Lactobacillus''. Finally, the brewer has the option of pasteurizing the wort by heating it to kill the ''Lactobacillus'' before adding the yeast for the main fermentation. Some creative brewers have applied wort souring techniques to longer aged [[Mixed Fermentation]] beers and barrel aged beers. Many brewers prefer this process over [[Sour Mashing]] because it can be easier to control, and when implemented properly it produces a clean sour beer in a short amount of time. The possibility of pasteurizing the soured wort also makes this a good method for making sour beers with a lot of residual malt sweetness (e.g. sour barley wines), and should also make it attractive to brewers who are concerned about infection issues in their cold side equipment (equipment that is used post-boil) <ref>[http://sourbeerblog.com/fast-souring-lactobacillus/ Miller, Matt. Dec 20, 2014. "Fast Souring with ''Lactobacillus'' – Best Practices, Sensory, & Science". Sour Beer Blog.]</ref>. When souring wort, some brewers first [[Wort_Souring#How_to_Pre-Acidify|lower the pH of the wort to 4.0-4.3]] before pitching ''Lactobacillus''. This has sometimes been found to help the head retention of the beer, and helps to protect the wort from contaminating microorganisms. For more information, see the [[Lactobacillus#Foam_Degradation|''Lactobacillus'' page section on Foam Degradation]].