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Added a "Contamination" section
<blockquote>"''Mixed culture fermentation for sour beers produces one thing, and (kettle souring) produces another thing. If you’re going to make a malty red ale that is kettle soured, don’t call it a Flanders Red. Honor the tradition.''" - Sean Burke of the Commons Brewery, Kettle Souring Presentation, CBC 2015.</blockquote>
==Contamination Concerns==
Contamination issues seem to be the biggest challenge with pre-souring wort with ''Lactobacillus''. This is because ''Lactobacillus'' does not fully ferment wort by itself (see [[100%25_Lactobacillus_Fermentation|100% ''Lactobacillus'' fermentation]]). When yeast fully ferments wort into beer, alcohol, hops, and a low pH all work together to help prevent other microorganisms from contaminating the beer (although contamination can certainly happen with beer spoilage microbes such as ''Brettanomyces'', ''Pediococcus'', etc.) <ref>[http://suigenerisbrewing.blogspot.com/2014/02/fact-or-fiction-can-pathogens-survive.html "Fact or Fiction? Can Pathogens Survive in Beer?" Sui Generis Blog. 02/18/2014. Retrieved 11/10/2016.]</ref>. When fermenting with ''Lactobacillus'' by itself, either no alcohol is produced or not enough alcohol is produced to have an antimicrobial effect. Usually hops are not used when souring wort with ''Lactobacillus'' because even small amounts of hops completely inhibit most commercial strains, so other microbes that are sensitive to hops are also not inhibited. The high available sugars and lack of alcohol/hops therefore increases the chances for contamination during souring wort with ''Lactobacillus''.
Contaminations can have a variety of effects on soured wort depending on the type of microbe(s) that caused the contamination. One typical off-flavor in kettle sour beers is [[Butyric_Acid|butyric acid]], which is in and smells like human vomit. Although the exact source of butyric acid in kettle soured beers has not been identified scientifically that we know of, butyric acid is produced by anaerobic contaminates and '''not''' when ''Lactobacillus'' is exposed to oxygen (see [[Lactobacillus#Effects_of_Oxygen|Effects of Oxygen on ''Lactobacillus'']] and [[Butyric_Acid|butyric acid]]). [[Isovaleric_Acid|Isovaleric acid]] is another off-flavor that can be produced by both anaerobic and aerobic contaminates.
Another very typical contaminate during souring wort with ''Lactobacillus'' is actually brewer's yeast (''S. cerevisiae''). Brewer's yeast is not greatly inhibited by ''Lactobacillus'', and ''Lactobacillus'' is greatly inhibited by the presence of active ''S. cerevisiae'' <ref name="Hubbe">[https://www.facebook.com/groups/MilkTheFunk/1407620505932826/ Effect of mixed cultures on microbiological development in Berliner Weisse (master thesis). Thomas Hübbe. 2016.]</ref>, and the warmer temperatures encourage ''S. cerevisiae'' to ferment the wort quickly. This often results in a beer that isn't sour because the ''Lactobacillus'' are out-competed by the yeast. Signs that yeast has contaminated the wort include the typical signs of yeast fermentation: the presence of a krausen, a gravity shift of more than 1.005 gravity points (or 0.5-1.0° Plato), and looking at a sample of the wort under a microscope. Sources of yeast contamination can come from poor sanitation, but they can also come from the yeast manufacturer themselves. See see [[100%25_Lactobacillus_Fermentation|100% ''Lactobacillus'' fermentation]] for more information.
===Preventing Contamination===
Several techniques can be applied to prevent contamination is kettle soured beers. Many of these are covered in the sections below when they apply to specific processes, however we will cover them all in this section as well.
Pre-acidifying wort to 4.5 pH or lower helps to kill many microbes that are not tolerant of low pH. Flushing the wort with CO2 during the souring process is thought to help prevent aerobic contaminates <ref>Private correspondence with Khristopher Johnson from Green Bench Brewing Co by Dan Pixley. 05/04/2016.]</ref>. Maintaining a temperature between 113-120°F (45-49°C) helps encourage some species of ''Lactobacillus'' and inhibits heat intolerant contaminates, however some species of ''Lactobacillus'' do not do well at these warmer temperatures (see the [[Lactobacillus#Culture_Charts|''Lactobacillus'' culture charts]]). Pre-boiling the wort has been shown to help greatly with preventing contamination. This is likely due to the killing power of boiling temperatures versus lower temperature pasteurization, as well as the heat and steam killing microbes on the sides of the boil kettle, the lid of the boil kettle, and the air space above the wort. Boil kettles are inherently unsanitary vessels compared to fermentation vessels, so great care should be taken to sanitize the vessel and prevent any air from getting into the vessel during the souring process. Air can get in when temperatures cool and a vacuum is created inside the kettle. Wrapping the boil kettle with plastic wrap has been a typical approach for homebrewers, as well as maintaining a constant temperature. Commercial brewers must also prevent air from getting sucked into the boil kettle. Some have used sanitized and inflated sports/beach balls or something similar to clog the boiler stack during kettle souring, for example.
Yeast contaminations can be difficult to avoid if they are coming from the manufacturer of the ''Lactobacillus'' culture. Look at the culture under a microscope and check for yeast cells, which will be much larger and circular in shape compared to the much smaller, rod-shaped bacteria. Yeast companies will usually offer a refund for any contaminated ''Lactobacillus'' cultures.
==Processes==