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'''Sour Worting''' is a process in which ''[[Lactobacillus]]'' 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 this method, 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. 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 sour worting, some brewers first [[Sour_Worting#How_to_Pre-Acidify|lower the pH of the wort to 4.50-4.83]] 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]].
Important note regarding aluminum pots: souring in an aluminum vessel may strip the aluminum of the protective oxide layer. The oxide layer is only stable at a pH of 4.5 - 8.5. Therefore, kettle souring in an aluminum pot is generally not recommended <ref>[http://www.pfonline.com/articles/aluminum-surface-finishing-corrosion-causes-and-troubleshooting Aluminum Surface Finishing Corrosion Causes and Troubleshooting. W. John Fullen, Boeing Research and Technology & Jennifer Deheck, Boeing, Seattle, Washington, USA. 10/17/2014.]</ref>.