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'''Wort Souring''' is the process of "[[Mixed Fermentation]]" (in the case of lactic acid bacteria being left alive to co-exist with yeast) or pre-boil acidfication (in the case of kettle sours) where lactic acid bacteria pre-ferment and acidify wort before yeast is pitched to complete the main alcoholic fermentation <ref>[https://www.researchgate.net/publication/341353855_The_power_of_sour_-_A_review_Old_traditions_new_opportunities Bossaert, Sofie & Crauwels, Sam & De Rouck, Gert & Lievens, Bart. (2019). The power of sour - A review: Old traditions, new opportunities. BrewingScience. 72. 78-88. 10.23763/BrSc19-10bossaert.]</ref><ref>[https://onlinelibrary.wiley.com/doi/full/10.1002/jib.569 Dysvik, A., Liland, K. H., Myhrer, K. S., Westereng, B., Rukke, E.-O., de Rouck, G., and Wicklund, T. (2019) Pre-fermentation with lactic acid bacteria in sour beer production. J. Inst. Brew., 125: 342– 356. https://doi.org/10.1002/jib.569.]</ref>. While non-sour beer falls in the range of 3.8-4.6 pH, a final pH between 3.0 and 3.7 is the general target range for the soured wort and also the finished sour beer ([[Titratable Acidity]] is more accurate for measuring perceived sourness). This is a broadly defined technique and there are many variations on souring wort. These include mixed fermentation methods such as souring in the primary fermenter for a short time period before adding yeast, or sequential fermentation such as souring in the boil kettle itself with a pure culture of lactic acid bacteria and then boiling to pasteurize the sour wort before yeast is added ('''kettle souring''') where the lactic acid bacteria is killed before yeast is added. There are also various methods of inoculating the wort with ''Lactobacillus''.