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Wort Souring

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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 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. Continuous flushing with CO2 can also help prevent a vacuum from sucking in air.
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.

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