How To: Brew a Kettle Sour
This is the first in a series of instructional posts I hope to do on basic and semi-advanced techniques in homebrewing. The goal of these posts is to provide quick, concise explanations of methods and ideas that newbie brewers may find confusing.
This one is going to focus on the concept of kettle souring, and how it can be used to produce a quick and easy gose or Berliner weisse-style beer. Most of the advice in this post is geared toward using malt extract, since that’s how I usually make my kettle sours, but I’ve tried to provide tips for all-grain as well.
What’s kettle souring?
Well, there are three kinds of sour beer:
- Accidental. The bad kind, usually caused by poor sanitation. You meant to brew a clean beer but ended up with something tart, funky, and possibly disgusting. Oops!
- Mixed culture. This is the kind that costs $15+ per bottle and tastes a bit like vinegar. It’s made by either fermenting a beer with “clean” saccharomyces yeast and then adding bacteria (lactobacillus and/or pediococcus) and Brettanomyces yeast. These sours take anywhere from several months to several years to develop, and possess complex flavors and aromas that only come with extended aging (often on wood). Old-school goses and Berliners were actually made this way.
- Kettle sour. This is the cheap, quick, and easy kind; less complex, but a whole lot easier. The basic concept? Add microbes to your wort before boiling, let them do their thing, and then boil to set the sourness level and sterilize your equipment.
What’s the difference between a gose and a Berliner?
In the US and other places that are not Germany, it’s basically just the presence of coriander and salt. Goses have them, Berliners don’t.
In Germany, the two styles have deep historical roots and more sharply defined style guidelines, but for homebrewers who aren’t fanatical about historical accuracy, it doesn’t really matter.
What do you need?
- Suitable wort. Goses and Berliners are both wheat beers. I like a mix of 3:2 pilsner to wheat, but 1:1 is ok too. You can use DME, LME, or all-grain, but all-grain is a little tricky because of the wheat content. Use rice hulls to avoid a stuck sparge. Aim for an OG of around 1.040, which should get you around 4% ABV. (Goses traditionally range from 4-5% ABV, while Berliners are weaker, around 3.5%.)
- A souring agent. You can use lacto from a commercial lab, but my preferred method is using GoodBelly StraightShots, which provide more than enough lactobacillus plantarum to sour a 5-gallon batch quickly and cheaply.
- Lactic acid. Grab a bottle at your local/online homebrew store to pre-acidify the wort.
- Plastic wrap. To seal the kettle.
- Hops. Entirely optional. Traditional goses and Berliners have very low hopping rates (typically <10 IBUs) because hops inhibit the souring process. But since we’re kettle souring and adding the hops after the microbes have already soured the beer, it doesn’t matter. If you want to make a hoppy gose, go for it!
- Yeast. A nice, clean ale yeast. Safale K97 (German Ale) and US-05 both work great. Two packages are recommended due to the acidity of wort. Something like White Labs 644 (Sacc Trois) might be good, too, if you want an even more citrusy result.
- Coriander seed and salt (gose only). Along with other flavorings, if you like.
What’s the process?
It’s really pretty simple:
- Prepare your wort. I’m generally an all-grain brewer, but when I make kettle sours, I use dry malt extract (DME) 90% of the time. It’s quick, easy, and in a light beer like this with a strong sour element, I don’t notice much difference in flavor vs. all-grain. If using DME, simply combine with your brewing water in your boil kettle and bring to approximately 170F. Hold it there for ~15 minutes to pasteurize. If you want to go all-grain, mash as usual, sparge if you’re sparging, and then raise your wort to 170F for 15 minutes to pasteurize it.
- Sour your wort. First, pre-acidify the wort with 10mL of lactic acid. This helps prevent any wild microbes from getting a foothold. Then, cover and chill to about 90F. Once in that temp range, toss in your lacto, close the lid on the kettle and seal it up. I like to use plastic wrap, since I already have it on hand, but you can use masking tape or whatever you like. Try to keep your kettle around 80-100F for the entire souring period, but it’s okay if it drops down into the 70s. NOTE: Some people recommend using CO2 to purge the headspace in the kettle, but research indicates this is generally unnecessary. Still, doing so won’t hurt anything, so feel free.
- Check the pH. After about 24 hours, un-seal the kettle and check the pH. You ideally want to be somewhere in the 3.2 to 3.5 range, depending on how sour you want it. (Lower is more sour.) If you don’t have a pH meter, just draw a sample and taste it, but bear in mind that the sweetness in the unfermented wort will make it taste less sour than it would be once the sugar gets fermented out. If all else fails, let it sour between 24 and 48 hours and you should be good.
- Boil the wort. When the wort is sour enough, it’s time to boil. Most Berliners and goses are very lightly hopped—often they have no hops at all. This means your boil can be very short. I like to boil mine for about 15 minutes, adding the hops at the start and the crushed coriander and salt at 10 minutes to go. (Feel free to throw in any finings, eg. Whirlfloc, at this point, too.)
- Chill and pitch yeast as usual. For a 5-gallon batch, I usually rehydrate two packets of dry yeast per package instructions (typically 10:1 tepid water to yeast by weight) and pitch the slurry.
- Ferment, add any fruit in secondary, and carb. Ferment according to package instructions. I typically keep my kettle sours around 68-70F until fermented out (usually 1.010ish FG). If I’m adding fruit and other adjuncts, I’ll do it in secondary (one of the few cases where I actually use a secondary fermenter), racking the finished beer onto to the fruit. When it comes time to package, I carb high—around 2.8 to 3.2 volumes of CO2.
Got a recipe?
Sure do! I call it Cheat Tart Gose. (If you want a Berliner-style beer, just make it 50/50 pils/wheat and ditch the coriander and salt.)
- Method: Extract
- Batch size: 5 gallons
- Boil: 15 minutes
- OG: 1.042
- FG 1.010
- ABV: 4.2%
- IBU: 8
- SRM: 2
The Grain (or Extract)
- 4 lbs Pilsner Malt
- 3 lbs Wheat Malt
- 3 lbs Pilsen DME
- 2 lbs Wheat DME
- 1.0 oz Saaz [3% AA] @ 15 minutes
- Yeast: 2x Safale K97, rehydrated
- Water: Whatever you like, doesn’t matter so much with DME (just watch out for chlorine). Distilled/RO is fine.
- Extras: 16oz Mango GoodBelly OR 2x GoodBelly StraightShot, 1 oz. crushed coriander seed @ 10 minutes, 0.75oz sea salt @ 10 minutes
Anything else I need to know?
People sure do love putting a ton of fruit (and other flavorful adjuncts) into goses and Berliners, myself included. Need proof? Look no further than the recently created Florida weisse and Catharina Sour categories.
The first time I made Cheat Tart Gose, I added nearly a pound of crushed lemongrass stalks and a bit under an ounce of Thai basil leaves to secondary. The flavor was phenomenal—bright lemony acidity with a subtle, herbal undercurrent. Later, I made a version with around 6 lbs of mango puree and a tincture of mixed New Mexico red chile and cayenne pepper. Also great, reminiscent of chili-mango candy. Most recently I made the same recipe, minus the coriander and salt, plus a ton of lime zest and toasted coconut. It was probably my favorite version to date.
If you like fruity beers, this is a great sandbox to play in. Try blueberries, raspberries, pineapple, lime or lemon zest, Buddha’s hand, durian, whatever! Herbs and spices work great, too. Typically, you should leave them in for 7 to 14 days and swirl the fermenter somewhat often to keep the fruit from floating and developing mold.
Good luck, and let me know how it goes!