Updated from our May 2018 club presentation (Dean V.). This is the quick, reliable way to brew tart beers like Gose and Berliner-style without barrels or bugs all over your brewery.
What is kettle souring?
Kettle souring means you sour the wort in your kettle, then boil to kill the bacteria, then ferment as usual. It’s fast (often 18–36 hours to target pH), predictable, and lower risk because the lactic acid bacteria never touch your cold-side gear.
Gear & supplies
- Normal brew setup (all-grain or extract)
- Lactobacillus source (pure culture, GoodBelly/probiotic, or grain)
- pH meter or good strips
- Food-grade lactic acid for pre-acidification
- Way to keep wort warm (90–115°F / 32–46°C) for a day
- CO₂ for blanketing the kettle (nice to have)
Why pre-acidify? Dropping the wort to ~pH 4.5 first suppresses spoilers and protects proteins, helping head retention later.
Step-by-step (5 gal / 19 L)
1) Make unhopped wort
Mash/lauter as usual (or make unhopped extract wort). Bring to ~10–15 min boil to sanitize, then chill to 95–110°F (35–43°C).
2) Pre-acidify
Add food-grade lactic acid to drop wort to pH ≤ 4.5. Stir and re-check.
3) Pitch lacto & protect from O₂
Pitch your culture (follow package/recipe). Purge headspace with CO₂ if possible and seal the kettle. Hold 90–100°F (32–38°C).
4) Sour to taste
Check every 6–12 hours. Target pH 3.2–3.6 (taste wins). Typical time 16–36 hours depending on culture and temperature.
5) Boil to finish
Bring to a rolling boil to kill lacto. Add light hops (5–15 IBUs) unless you’re brewing a salt/coriander-forward Gose with minimal bitterness.
6) Ferment clean
Chill and pitch a neutral ale yeast; ferment cool and clean. Fruit, salt, or spices go post-fermentation or near the end of fermentation.
Culture options (what to pitch)
- Pure lacto cultures (best control and speed)
- GoodBelly / probiotic blends (very workable, budget-friendly)
- Handful of grain (works but less predictable)
Dean’s tip: A blend of lacto strains broadens the temp range and rounds the acidity; pre-acidify to pH ~4.5 first.
Targets & timing (quick reference)
- Pre-acidify: pH ≤ 4.5
- Hold temp: 90–100°F (32–38°C)
- Finish pH: ~3.2–3.6 (taste!)
- Sour time: 16–36 hours, commonly ~24 hours
- Boil bitterness: 5–15 IBUs, gentle
Troubleshooting
- Butyric (vomit/cheese): oxygen got in or temp too low. Purge, seal, and keep it warm; mild aromas usually boil off.
- Stalled souring: bump temp within range; ensure pH pre-drop; pitch fresh culture.
- Flabby/no head: don’t skip pre-acidify; keep IBUs low until after souring.
Two club-tested starting points
Base Gose (Dean’s template)
Clean, crushable; add sea salt and coriander to taste. Uses probiotic blend for quick 24-hour souring.
Key Lime Gose (community favorite)
Follow the kettle-sour method above; add lime zest/juice after fermentation; keep bitterness minimal.
References & further reading
- CBC 2015: Kettle Souring @ Breakside Brewery (process, temps, CO₂ purge, timing)
- Colorado Brewers Guild: Basics of Kettle Souring (why pre-acidify, definitions).
- LDB recipes & posts: Dean’s Base Gose; Key Lime Gose; club archive.