Sour Worting
Contents
Introduction
Sour Worting is a process in which Lactobacillus is given a "jump start" to creating lactic acid in a batch of wort before the primary fermentation is started by pitching yeast. There are several variations on this method, including souring in the boil kettle or another vessel besides the primary fermenter, and souring in the primary fermenter. There are also variations on how to add Lactobacillus to the wort, as well as choosing whether or not to heat pasteurize the wort before adding it to the primary fermenter. Many brewers prefer this process over sour mashing because the process can be easier to control. When conditions are controlled properly, a clean sour beer can be produced very quickly.
Processes
Souring in the Boil Kettle
The process of souring in the boil kettle is a simple process that is often used if the brewer wants to heat pasteurize the wort. Pasteurizing the wort has the advantage of allowing the brewer to rack the pasteurized wort into a fermenter and pitch brewer's yeast without fear of an ongoing infection in their post-boil equipment.
The brewing process is the same for any all grain brewing process up until the first wort and sparge runnings are collected into the boil kettle. The temperatures that a typical mash out/sparge reach should be enough to pasteurize the wort[1]. Once all of the wort is collected in the boil kettle, the wort is chilled to around 80-120°F (37-48°C), depending on the Lactobacillus culture that is being used. Once chilled to the temperature that is appropriate, the brewer pitches their culture of Lactobacillus directly into the kettle. 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 (not just Lactobacillus; the temperature and low level of oxygen in the wort however favors Lactobacillus). 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.
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[2]. The wort may be boiled normally in the case of any style of beer that requires a longer boiling process, or it it may not 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 [1], 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 safely be 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 3.5 or lower, the acidity of the wort can effect the fermentation of some strains of brewer's yeast. 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.