Lactobacillus plantarum
Various (probiotic capsules) · bacteria · Capsule or liquid culture
A souring bacterium, not a yeast. Used to sour wort in the kettle before the boil — fast, clean lactic acidity, and because the boil kills it afterwards it never reaches the cold side or the brewery's equipment.
1 brew
About
The workhorse of kettle souring. Lactobacillus plantarum converts wort sugars to lactic acid, producing a clean, bright tartness with none of the funk of a mixed culture. It is hop-sensitive, so souring happens in unhopped or barely-hopped wort before the boil; the boil then kills it, which is what makes kettle souring safe to do on ordinary clean equipment. Commonly sourced from probiotic capsules rather than a brewing lab, which is cheap and works well — the strains sold for gut health are the same species. Note that souring consumes fermentable sugar, so a kettle-soured wort finishes lower in alcohol than its original gravity suggests.
Specs
- Attenuation
- n/a — produces lactic acid, not alcohol
- Flocculation
- n/a
- Temperature
- 32–45°C
- Optimal
- 35–40°C (faster souring, and outgrows spoilage organisms)
- Ferment time
- 24–72 hours to reach pH 3.2–3.5
- Pitch rate
- Enough to acidify — commonly 8–12 probiotic capsules for a 25 L batch
- Form
- Capsule or liquid culture
Recipe pairing
- Grains
- Pilsner and wheat — the classic Berliner Weisse grist. Keep it simple and fermentable
- Hops
- Almost none pre-boil; Lacto is inhibited by even low IBUs. All hopping goes in the post-souring boil
- Adjuncts
- Fruit pairs naturally; add late in fermentation for biotransformation rather than post-ferment for raw flavour
- Suited to
- Berliner Weisse, Gose, Kettle Sour, Fruited Sour
Brewing tips
- Pre-acidify the wort to about pH 4.5 before pitching. It gives Lacto a head start over spoilage organisms and is the single biggest factor in a clean sour.
- Purge the headspace with CO2 and cover the wort. Lacto is happiest without oxygen, and the cover keeps everything else out.
- Hold the souring wort warm — 35–40°C is much faster than room temperature and more selective.
- Track pH, not time. Stop at 3.2–3.5 for a drinkable sour; below 3.0 is aggressive and hard on the yeast that follows.
- Boil after souring to kill the Lacto. That is what stops the acidity moving and keeps the bacteria off your cold-side gear.
- Expect to double-pitch the primary yeast — low-pH wort is stressful and ale strains struggle in it.
Handling & storage
- Rehydration
- Direct-pitch the capsule powder into wort held at souring temperature.
- Storage
- Refrigerate capsules; check the date.
- Shelf life
- To the capsule's printed expiry.