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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>.

Souring in the boil kettle is a simple process that is often used if the brewer wants to subsequently heat pasteurize the wort. Pasteurizing the wort has the advantage of allowing the brewer to rack the pasteurized wort into a fermenter and pitch brewer's yeast without fear of an ongoing Lactobacillus infection in their post-boil equipment.

Once the soured wort is heat pasteurized, it can be safely added to the primary fermenting vessel without worries of future infections. The wort is aerated as normal, and brewer's yeast, or [[Brettanomyces]] yeast is then pitched into the wort as normal (usually brewer's yeast is used if infection of equipment is a concern). At a pH of 3.4 or lower, the acidity of the wort can effect the fermentation of some strains of brewer's yeast <ref name="low ph">[http://www.homebrewtalk.com/f127/no-hop-berliner-weisse-415067/index3.html#post5280971 Michael Tonsmeire on HBT]</ref>. It is recommended to pitch a healthy starter of yeast. In the case of using dry yeast, re-hydrating as per the manufacturer's recommendations and using a yeast nutrient like Go-Ferm is recommended.

Wort can be soured in the primary fermenter before adding other yeasts. This is generally a good approach for brewers who aren't concerned with pasteurization and infections of their cold side equipment. This has the advantage of possibly producing a more complex sour beer overall, or at least a sour beer that will evolve over time. It has the advantage over a more traditional [[Mixed Fermentation]] in that Lactobacillus is used to guarantee at least a certain level of sourness. This is also a good process to use for making a [[Berliner Weissbier]].

After the desired acidity level is reached from the incubating Lactobacillus bacteria, the brewer can crash cool the fermenter down to the temperature that is desired for the primary fermenting yeast. Both [[Saccharomyces]] and [[Brettanomyces]], or a blend can be used as primary fermenting yeast. Brettanomyces is often chosen because of it's higher tolerance of a low pH environment (3.4- pH <ref name="low ph">[http://www.homebrewtalk.com/f127/no-hop-berliner-weisse-415067/index3.html#post5280971 Michael Tonsmeire on HBT]</ref>). If the chosen yeast requires aeration and the brewer has the ability, the sour wort should be aerated before pitching yeast. [[User:DanABA|DanABA]] has had good luck using Safale US-05 dry yeast in non-aerated wort; it is recommended that US-05 is re-hydrated in warm water with a re-hydrating yeast nutrient such as Go-Ferm <ref>[http://www.scottlab.com/product-102.aspx Go-Ferm]</ref>. The wort is then fermented out as normal. The brewer can consider other [[Brewing Methods]] such as pitching Brettanomyces, a mixed culture, or commercial sour beer dregs into secondary.

This process is very similar to sour worting in the kettle. This method is ideal for those who wish to use grains to introduce Lactobacillus to the beer. If done properly, the formation of [[Butyric Acid]] and [[Isovaleric Acid]] should be minimal.

James Spencer provides an article that fully explains his process, as well as a step by step video guide and tasting on Beer and Wine Journal <ref name="james_spencer" />.

[[File:Green_man_berliner.jpg|thumb|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>

In general, non-fat Greek yogurt that is unpasteurized works best. Brands of yogurt that have been reported to be successful with this method:

* Fage Yogurt <ref name="yogurt1">[https://www.facebook.com/groups/MilkTheFunk/permalink/1022780907750123/ Mark Fry on the MTF Facebook group. 2/19/2015.]</ref>

* Nancy's Yogurt <ref>[http://www.notsoprofessionalbeer.com/2013/09/brewing-with-yogurt.html?m=1 ''Brewing with Yogurt''. The Not So Professional Beer Blog. Retrieved 3/3/2015.]</ref>

* [http://www.notsoprofessionalbeer.com/2013/09/brewing-with-yogurt.html?m=1 ''Brewing with Yogurt''. The Not So Professional Beer Blog.]

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[[Category:Techniques]]