Kettle souring has become an incresingly popular brewing method that allows the brewer to produce sour beer in a relatively short amount of time. Kettle sours are often seen as “one dimensional” compared to traditionally soured beers, but are great vessels for practice and experimentation and can make an exceptional product when done correctly. Below is an outline to my method of kettle souring. It assumes that the reader already knows how to brew all-grain, and is looking to expand their arsenal of brewing techniques.
The difference between brewing clean and kettle soured beers is the addition of LAB (lactic acid producing bacteria) before primary fermentation. In many methods (including this one), you will boil your wort to kill off bacteria in order to avoid the risk of “contaminating” your equipment.
Assemble equipment/recipe/ingredients. Berliner Weisse and Gose are two common styles brewed with this method. Each are intentioanlly sessionable and receptive to fruit/spice additions, so they are exellent styles to practice/experiment with. Many brewers don’t use hops in their kettle sours.
Mash, vorlauf, and lauter into your boil kettle as usual. Consider mashing low to produce more fermentable sugars.
Bring your wort to a boil, or close to it. Hold your wort at a minumum of 180F for at least 10 minutes (boil it if you are looking for some peace of mind) to kill whatever bacteria may have survived the mash. The goal is to sour with exclusively the intended bacteria.
Cool your wort. Plate chillers or copper immersian chillers work very well to cool down wort quickly. Each bacteria strain performs differently in different temperatures, but most are optimal in the 100-120F range (LAB sources will be posted later).
Pitch your bacteria. Once your wort has cooled, pitch your bacteria into the kettle. There are two main goals at this point: to maintain temperature, and to limit exposure to oxygen. If you have co2 handy, purge the headspace thorouhgly and then use plastic wrap or tinfoil to keep as much oxygen out as possible. If you don’t have co2 available, rest plastic wrap on top of the wort (think like you do to avocados). As far as maintaining temperature, heating wraps are available to purchase online or from your local homebrew store, although blankets/insulation work just fine. Many homebrewers will simply leave their kettle on the burner and fire it up at different intervals to raise the temperature back up. ** If you are brewing a larger (more than 5 gallons) batch or are using swansons/goodbelly, you may not need to worry about the temperature drop.
Wait. LAB typically takes between 24-48 hours to reach desired level of sourness. Feel free to measure pH periodically (every day or so), although I have had success with both 24 and 48 hour souring. The longer you wait, the more you risk oxygen exposure and thus the production of off flavors.
Complete your brewing as you would a clean beer. Bring your wort back up to a boil to kill off the bacteria making to avoid “contaminating” your equipment, add hops, cool, pitch yeast, etc. Kettle soured beers take roughly the same amount of time to ferment as a clean beer. Keg or bottle your result, and enjoy!
Sourcing your Bacteria:
Goodbelly Probiotic– This is my preference when brewing kettle sours. The mango variety offers the most neutral result, while the fruited ones contribute more or less depending on their flavor. I have been able to find the 32oz cartons in my local Safeway Supermarket, and have had a lot of success pitching 32oz per 5 gallons wort.
Swanson’s L. Plantarum – reasonably priced on Amazon and truly offers a neutral flavor. I’ve used 10 pills to 5 gallons with success.
Commecial Pitches – Whitelabs, Wyeast, Omega, and Gigayeast all have reliable pitches. Whitelabs and Wyeast are more likely to be available at your local homebrew store. They come in capsules/bags specifically for 5 gallon pitches.
Other options – Yogurt, unmilled grains (malted barley), kefir, sourdough. All of these are viable options with more info on each of them here.
I tend to go for the probiotics because they are cheap, available locally, and contain mostly L. Plantarum – a bacteria that performs well even as the wort cools down.The Milk the Funk Wiki has a ton of good info about different lacto strains and their effectiveness in different temperatures.
Best of luck, and happy brewing!