Changes

When working with lactic acid-producing bacteria, the brewer’s goal is usually to attain clean-tasting sourness, while obtaining desirable flavor contributions from these bacteria, and simultaneously minimizing off-flavors. It should be noted that off flavors span the range from undesired by most, to desirable to some. For example, isovaleric acid is a compound known for its footy aroma that would be considered an off flavor in many beers, yet it gives a highly desired flavor to certain French cheeses and is aceptable acceptable by some in small amounts in mixed fermentation beer.

With that said, contamination issues are among the biggest challenges when 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 prevent most spoilage 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, but they also inhibit some spoilage microorganisms. The high available sugars, warm temperatures typically used in souring wort, and a lack of alcohol and hops therefore increases increase the chances for contamination during souring wort with ''Lactobacillus''.

Another source of contamination, which is arguably desired, happens when using a "wild" source of ''Lactobacillus''. For example, when culturing ''Lactobacillus'' using non-plating techniques from grains, fruit, or from some other fermented food such as kefir, sauerkraut, etc., yeast and other microbes can carry over from the culturing process (see [[Alternative Bacteria Sources]]). The only way to guarantee that only ''Lactobacillus'' from a "wild" source such as these ferment the wort, is to isolate the microbe using plating techniques (see [[Wild Yeast Isolation]]). Otherwise , there is a chance that wild yeast will also survive the culturing process.

Several techniques can be applied to prevent contamination in 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 head 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 and lid with plastic wrap has been a typical approach for homebrewers, as well as maintaining a constant temperature so as to avoid creating a vacuum inside the kettle from cooling temperatures. 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. Continuous flushing with CO2 can also help prevent a vacuum from sucking in air. Finally, achieving the desired acidity as quickly as possible helps to cut down on the chances for contamination. Achieving the desired acid development within 48 hours is an ideal goal, but achieving it within 12-24 hours is even better.