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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 (see the ''[[Lactobacillus]]'' page for suggested temperatures and times for specific strains). The kettle lid should be firmly in place and optionally sealed with plastic wrap so that other microorganisms do not get in. Potential for 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. 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 (this is called [http://www.garshol.priv.no/blog/331.html Raw Ale]). Heat pasteurization should kill the ''Lactobacillus'' culture being used to sour the wort <ref name="pasteurization" />. '''Caution: the wort gravity may also be tested to check for alcohol presence, which commonly happens when the soured wort was contaminated with yeast (see [[100% Lactobacillus Fermentation]]). Alcohol can be more easily boiled off since it boils at 173.1°F or 78.4°C <ref name="boiling_of_alcohol">[http://chemistry.about.com/od/moleculecompoundfacts/f/What-Is-The-Boiling-Point-Of-Alcohol.htm Boiling temperature of ethanol]</ref>.''' ''Lactobacillus'' will not ferment wort more than ~1.005 gravity points, or 0.5-1°P, regardless of the wort's starting gravity (see [[100% Lactobacillus Fermentation]]). If the wort fermented out due to a yeast contamination, then the brewer should consider not boiling the wort (which would technically be beer at this point) and heat pasteurizing instead. Boiling and high pasteurization temperatures will not only evaporate alcohol, but will also affect the flavor of the beer. Beer already has anti-bacterial properties, such as low pH, presence of alcohol, and hops (although hops may not be present in wort being soured). For these reasons, the beer industry commonly heat pasteurizes beer at 140°F/60°C for 15 minutes, and this is also adequate for pasteurizing soured wort/beer <ref>[http://www.sciencedirect.com/science/article/pii/S0023643806002854#bib16 A suitable model of microbial survival curves for beer pasteurization. Sencer Buzrul. 2006.]</ref>.
Once the soured wort is boiled or 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 cold side equipment is a concern). At a pH of 3.4 or lower, the acidity of the wort can reportedly 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, possibly with a higher cell count than normal. 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. Many yeast strains have been successfully used by MTF members to ferment pre-acidified wort: US05, S04, WY1098/WLP007/OYL-006, Belle Saison, Sacch Trois, Bret brux, B. clausenii, B. custersianus, Bret Drie (BSI), WY3711, and WY3726 to name a few (see reference) <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1105185972842949/ Conversation on MTF about using specific yeast strains in acidic wort. 7/6/2015.]</ref>.