The Box

Kettle sour process

brewing fermentation france

Summary

Notes and resources on making kettle soured beer (with Lactobacillus Plantarum).

Process

1. Starter

Make a starter with your bacteria (kindly referred to as "bug" below) of choice (1-2 days before brew day).

  1. Sanitize an erlenmeyer of 2/3 liters
  2. Boil water and extract to prepare 1L of wort at 1.040 OG
  3. Seal loosely with alfoil
  4. Cool down to 25-30 celsius
  5. Put your bug in the starter and make sure temp stays within 20-30 degrees
  6. Seal loosely with alfoil

Magnetic stirring is better (felt more vigorous) but I've done 2 brews without and it was fine.

It's ready in about 24 hours, 48 if the bug was slow (old pills, not enough pills etc). It should look hazy, smell acidic/lactic/clean yoghurt. More on "how do you know the starter is ready" on the Milk the Funk wiki.

2. Brew day, part 1 (mash + short boil)

  1. Mash as per usual
  2. Boil 10-15 minutes (depends on the recipe, but the important bit is to stop the mash enzymes so you could reduce that time probably)
  3. Cool down to bug-friendly temperature (30 celsius +/- 5)
  4. Measure wort pH
  5. Innoculate kettle with your started bug. DO NOT FORGET TO REMOVE THE MAGNETIC STIRRER METAL BIT from the erlenmeyer before chugging the starter in the kettle
  6. Close the kettle lid, seal loosely with with alfoil or cling wrap

Temp control: stay within the 30 +/- 5 celsius range. I usually let it on the kitchen counter without extra temp. control but depends on the season. Plantarum doesn’t care that much.

3. Souring (24-48 hours)

Take pH readings regularly. I sanitize a spoon, open the kettle, stir a little bit, then take a small sample to read the pH from

Up to you to decide when you're sour enough. That's what I like about kettle sours, you stop the souring when it suits you by going to the boil (also means you have to be ready to restart the brewing process). I go for a pH of [3.1-3.2]. 3.3 is acceptable, 3.0 is the lower limit of acceptable according to some. In Melbourne, with Feb/March temperatures, souring took about 24-36 hours for me.

4. Brew day, part 2 (boil + the rest)

  1. Remove foil, get the kettle to the boil and brew as per usual
  2. Ferment with your yeast of choice. I've used US-05 once and Kveik twice for my Berliner Weisse. I'll probably use Kveik all the time in the future.

Lactobacillus Plantarum

More notes

No hops before the souring process. Apparently it inhibits the bugs.

Resources