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[[File:Green_man_berliner.jpg|thumb|Mike Karnowski from Green Man Brewery Blueberry Berliner Weisse made from a yogurt starter]]''Yogurt Souring'' refers to the method of souring wort using unpasteurized yogurt. Greek yogurt is often made with ''Lactobacillus acidophilus'', a lactic acid producing bacteria that is also associated with some health benefits <ref>[http://en.wikipedia.org/wiki/Lactobacillus_acidophilus Lactobacillus acidophilus Wikipedia page. Retrieved 3/3/2015.]</ref>. Using cultures of ''L. acidophilus'' from yogurt reportedly can make a 3.0-3.5 pH sour wort in 24 hours, without producing vomit/fecal flavors and aromas. To sour 5 gallons of wort with yogurt, make a 1 liter batch of unhopped starter wort the day before brew day. Add 2-4 teaspoons of live yogurt to the starter wort. Maintain a 100-110°F (37.8-43.3°C) temperature for about 24 hours. On brew day, and after the 24 hour sour starter is finished, mash and sparge a low IBU wort as normal, boil for a few minutes, and then chill the wort down to 100-110°F (37.8-43.3°C). Pitch the yogurt starter into the wort, and hold the temperature as close to the 100-110°F (37.8-43.3°C) range as possible. Bubbling CO2 through the wort is advised if possible to prevent potential off flavors, but is not required. Within 24 hours, the wort should be down in the 3.x pH range. Boil the wort, adding any hops that the recipe calls for, yeast nutrient, etc., and then cool the wort down to Saccharomyces pitching temperatures. Bob's your uncle! <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1029598090401738/?comment_id=1030074730354074&offset=0&total_comments=25 Conversation with Mike Karnowski of Green Man Brewery on the MTF Facebook group. 3/3/2015.]</ref>