This is a quick kettle sour. It's ideal for anyone who doesn't want to risk "contaminating" their brewing equipment with bacteria.

Make up a lacto starter (I use Water Kiefer as the source *).
Mash as normal and bring to the boil, then flameout immediately and allow to cool down 38 C. Pitch lacto starter and purge kettle headspace with CO2. Maintain temp. Sample every 12 hrs or so to monitor lacto progress. Once it's sour enough, bring the kettle back up to the boil and continue your brewing process as normal.

• Lacto Starter Method
  Combine the following ingredients to a liter of filtered water and boil for 15 minutes:
  90 grams Dry Malt Extract
  20 grams Dextrose (Glucose)
  10 grams Calcium Carbonate (CaCO3 / chalk)
  1 gram Yeast Nutrient or DAP (diammonium phosphate)
  
  
  • Cool this starter solution down to the temperature and add 100 ml of filtered water kefir.
    
  • Seal the flask with a rubber stopper and airlock to prevent additional oxygen from entering the starter solution.
    
  • Let it stand (covered) until pH reaches about 3.4 (5 days in my case), it will vary a lot depending on room temp.
    
  • If you have a means of providing a temperature controlled environment, optimal growth is typically between 30 and 40 C.