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If a pure culture of Lactobacillus bacteria is used it is ideal but not necessary to fill the head space of the fermenter with CO2 gas (some brewers have reported that this will help reduce sulfur in the finished beer). The kettle should be held at the desired temperature for 24-72 hours (in some cases longer, but no longer than 5 days). Depending on the strain of Lactobacillus, and the desired sour level, the time of incubation is ultimately a variable that is up to the brewer. The kettle lid should be firmly in place and optionally sealed with plastic wrap so that other microorganisms do not get in. Potential formation of [[Butyric Acid]] and [[Isovaleric Acid]] when using only a pure culture is extremely slight to none assuming no other microbes are allowed inside the kettle.
Once the level of acidity is reached (this can be tested with a reliable pH meter, or in the case of using a pure culture can safely be taste tested), the wort is brought to a boil. ''Caution: the wort gravity may also be tested to check for alcohol presence. Alcohol can be more easily boiled off since it boils at 173.1°F or 78.37°C <refname="boiling_of_alcohol">[http://chemistry.about.com/od/moleculecompoundfacts/f/What-Is-The-Boiling-Point-Of-Alcohol.htm Boiling temperature of ethanol]</ref>.'' The wort may be boiled normally in the case of any style of beer that requires a longer boiling process, or it it may be boiled for no more than a minute or two in the case of making a [[Berliner Weissbier]]. Technically speaking, the wort doesn't need to be boiled at all, as long as it is heat pasteurized <ref name="pasteurization" />, so if alcohol is present then the brewer can choose to heat pasteurize the wort at 170°F (76.6°C) for 15 minutes.
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.
The wort is mashed and sparged as normal, and is then lowered to somewhere between 113°F-120°F (45°C-48.8°C). This temperature favors Lactobacillus, while discouraging Enterobacteriaceae. Optionally, the mash pH can be lowered to 4.5 with lactic acid or acidulated malt to further discourage Enterobacteriaceae activity. Once the desired temperature (and optionally pH) is reached, a handful of fresh malted unmilled grain is added to the mash and allowed a few minutes to inoculate the mash with the microbes found naturally on the grain husks. The wort is then transferred to a second vessel such as a glass carboy. The vessel should be filled to the very top, minimizing the oxygen levels inside the vessel. The vessel should be stored in a heated environment that maintains a temperature between 113°F-120°F (45°C-48.8°C) for 1 to 4 days depending on how much acidity the brewer wants (3 days is a good rule of thumb).
Once the 1 to 4 day time period has been reached, the wort is transferred to the boil kettle and boiled as normal. Boiling will kill all of the microorganisms in the wort, and will provide the option for adding hops and other kettle additions. Just as with kettle souring, the wort doesn't have to be boiled, but can be instead heat pasteurized at 170°F (76.6°C) for 15 minutes<ref name="pasteurization" />. ''Caution: the wort gravity may also be tested to check for alcohol presence. Alcohol can be more easily boiled off since it boils at 173.1°F (78.37°C)<ref name="boiling_of_alcohol" />.'' Once boiled, the wort can be chilled and handled in the same way as the above methods for wort souring. 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>[http://beerandwinejournal.com/sour-wort-berliner/ Spencer, James. December 15, 2014. Beer and Wine Journal.] </ref>.
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