Kettle Souring with a Heating Element
TroubleShooting
Kevan McCrummen - Coeur d’Alene, Idaho asks,
I want to try kettle souring but am concerned about contamination. I have a 10-gallon (38-L), three kettle, indoor electric brewery. I’m wondering if it’s possible to transfer the sweet wort to my boil kettle for souring instead of a separate heated fermentation vessel. Is it reasonable to maintain 100 °F (38 °C) via electric heating element in the kettle over the 24 to 72 hours, or would the element kill Lactobacillus every time it cycled on? Other than keeping bottling/ kegging/ dispensing equipment funk free (don’t get me wrong - that’s great), I don’t see the benefit to the brewery of transferring the wort to a fermenter to sour. The fermenter, pump and hoses would be exposed to Lactobacillus as the wort travels back to the boil kettle. If I could avoid that contamination by leaving the wort covered in a well-sanitized boil kettle, blanket with CO2, and use a heterofermentative Lacto (which would continue producing CO2), then no other equipment would have contact and I could simply bring it to a boil when target pH was reached.
Kettle sours have become quite popular with commercial craft brewers who want to brew sour beers without turning their breweries into funk factories and the technique really works quite well. It’s also a really fast way to produce these styles. The main downside for commercial operations is having the brew kettle tied up for 2–3 days during the souring process, but this is really not a big deal for most homebrewers. I know of several breweries doing this using vessels that are steam heated and insulated; from what I have seen and tasted at these breweries there is really nothing to worry about when using heating elements to keep the sour wort warm. Electric heating elements are certainly a bit different than steam, but as long as you are using a low density heating element and controlling the temperature of your wort in the 90–110 °F (32–43 °C) range you will not be killing many cells in the process. You need not worry about killing your bacteria using this method!
I totally agree with your assessment that there is no benefit to moving wort from the brewhouse into your fermenter for the souring step, and that in eliminating this extra step you are also reducing the risk of problems in the future from bacteria. Speaking of steps, I suggest adding two steps to your proposed plan. The first is a short boil to sterilize your wort, just as you would with any other brew. And the second step is wort cooling to bring the wort temperature into the 90–110 °F (32–43 °C) range. This step allows you to control what is growing in your wort.
Your plan to use heterofermentative lactic acid bacteria, such as Lactobacillus brevis, to keep the headspace blanketed in carbon dioxide sounds good. These strains are also reported to do a better job with souring than homofermentative strains like Lactobacillus delbrueckii. It seems that most brewers are using pH to monitor the souring process and arrest souring (by boiling their wort) when the pH is in the 3.2–3.6 range. Two things to be mindful of with the sour wort are yeast strain and nutrient content. Some yeast strains don’t do very well in low pH environments, so if you are having troubles with fermentation consider changing yeast strain. Lactic acid bacteria do consume nutrients during the souring process and it may be beneficial to add a moderate dose of yeast nutrients to your wort after souring is complete. There is a lot of trial and error experimentation going on with these beers, so keep your eyes and ears open to what other brewers are doing and feel free to venture down your own path and figure out what works best for you in terms of producing the type of sour beer flavor that you personally like.
