Since we got our new system, I can finally start doing sours again! Specifically, kettle sours. If you’re unfamiliar with a kettle sour, it is a process that can be used to make quick, clean sour beers in a controlled manner. Beers such as Berliner weisse and gose can be made with the kettle sour method, using a bacteria called lactobacillus that creates lactic acid very quickly.
Gose (pronounced goes-suh) is a style I am very interested in exploring. Our second big batch of gose is coming up. Resaca Lima is a gose made with limes and pink Himalayan salt. Gose is an old style of German wheat beer that has a light level of salt, tartness, and clean fermentation character. The taste is really nice–a lot of refreshing flavor at only 4% ABV. We’ll have other variations all summer long–Resaca Naranja, made with navel oranges, and Resaca Negra, a dark version.
You may have already tried some commercial goses that have cropped up over the last year. Some of these beers are made by adding food grade lactic acid to the beer, vs. using lactobacillus to sour. The difference is that beers soured with lactobacillus have a softer, more complex flavor. You get less harsh acidity and touches of lemon and white wine. I think it makes a much better beer.
So, how does the process work? I’ll explain now in-depth, in case you want to try this at home or on a professional scale. Whichever the case, I highly suggest that you join the Facebook group Milk the Funk. It is a great resource of home and pro brewers focused on sour beer production. There is a fantastic wiki that brings a more scientific approach into an area of brewing that is too often left to random chance.
To kettle sour, you first perform a standard mash and transfer your wort to your boil kettle. After that, you bring your wort to a boil, then chill to the appropriate temperature for the lactobacillus strain you are using. Then, you add your lacto, close up your kettle, and let it sit at the correct temperature until you hit your desired PH. After that, you bring to a boil, chill, and transfer to your fermenter. The beer is capped at the desired PH, and the lacto is killed so that you don’t run any through your other equipment.
Simple enough. Some other key information…
First, lactobacillus shouldn’t form a krausen. If you see one, you probably have an unwanted organism at work, which probably means your beer is wrecked. If there is a stomach acid or cheesey aroma, it should be dumped. Number two, it isn’t necessary to purge oxygen from the beer before adding your lacto. Some people think it prevents isovaleric acid or butyric acid from being formed. Those are caused by other organisms such as clostridium, not by lactobacillus. Third, it’s pretty hard to overpitch lacto, but you can underpitch, so a big starter is a good idea. Lastly, the most important part of a kettle sour is a clean kettle. Without a sparkling clean kettle, you are running a serious risk of contamination. Many things will out-compete lacto and ruin your beer, so keeping things as clean as possible is integral.
My current favorite lacto strain is plantarum. It works well at 85-95 degrees, so it’s a good option for homebrewers. It can even work lower than that. It’s also easily available in probiotic drinks and supplements such as Goodbelly or Swanson’s probiotic pills. I’ll take a bottle of 30 Swanson’s pills, and dump it in a 5 liter starter and let it sit for three days before pitching the entire thing in to a 3 BBL batch. Plantarum will naturally cap out at 3.2-3.4 PH, so no need to worry about it over-souring. I will go ahead and start to boil when it gets under 3.4. For a gose, 30 grams of salt per 5 gallons is the perfect amount to add during the boil.
I will do a 15 minute boil to make sure everything is hopefully dead in the beer and drive off a little DMS. Afterwards, just chill the wort and transfer to your fermenter. For a gose, you should select a neutral ale yeast. US-05 is perfect.
Checking gravity is a bit difficult because lactic acid is dense and interferes with readings. I still need to look into how to check gravity…I’ve noticed that fermentation appears a bit more sluggish on kettle sours with US-05, maybe since the acidity inhibits the yeast a little bit. Other strains such as French saison have no problem, though.
I’m really happy with our gose, and I think it is a terrific example of a style that I really enjoy!