Changes

There are various ways of inoculating the wort. A reliable method is pitching a pure culture of Lactobacillus, or a blend of Lactobacillus cultures. Alternatively, a handful of unmilled malted barley can be added to the kettle for inoculation instead of a pure culture, since the husks of grain carry many microorganisms. If unmilled grain is added, it is recommended to fill the head space of the kettle with CO2 because oxygen can encourage off flavors such as rancid cheese from [[Butyric Acid]] and/or [[Isovaleric Acid]], which are produced by microbes that are naturally present on the grain. Keeping the temperature between 113-120°F (45-48.8°C) will encourage the Lactobacillus resident on the grain and will discourage other bacteria. Lowering the pH of the wort to under 4.4 will also discourage many other bacteria from thriving in the wort during the incubation period. There currently is no formula for how much lactic acid to add to a volume of wort due to the different buffering capacities of wort and water, but using 1ml 1 ml of 88% lactic acid per .1 shift in pH for 5 gallons of wort is a good starting measurement. Consider [[Alternative Bacteria Sources]] for more reliable approaches to using "wild" Lactobacillus, or Lactobacillus from sources other than yeast labs.

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. ''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 78.4°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>.'' 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]), 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 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 <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1105185972842949/ Conversation on MTF about using specific yeast strains in acidic wort. 7/6/2015.]</ref>.