Beginner's Guide to Kettle Souring with BIAB / Electric setup

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Hi AHB members,

After a lot of research and much thought I have just completed my first Brew In A BAG (BIAB) sour kettle using the ‘wild’ lactobacillus found on grain as opposed to cultures made by Wyeast / White Labs. I am so far very happy with the outcome and thought I would share my experiences / technique in case it is of use to others.

For those interested in reading the source material I have found the following resources to be very helpful and informative:





American Sour Beers: Innovative Techniques for Mixed Fermentations
Written by Michael Tonsmeire

Sour Mash Berliner Weisse by Basic Brewing

The Sour Hour Episode 4 (kettle sour beers) by The Brewing Network

I found that I spent a lot of time researching because there are many different and conflicting opinions on the best way to kettle / mash sour and whether or not it is safe / viable to sour with wild bacteria as opposed to cultivated pitches. I personally was curious and decided to take on the challenge to see for myself.

The sour kettle technique seems to be particularly suited to BIAB/Electric due to BIAB/Electric’s ability to set and hold a particular temperature for an extended period of time. While I am sure these techniques could be adapted to other systems for the purpose of this post I will assume BIAB. It should also be noted that this technique does not put any of your equipment at risk of contamination (hot-side nasties are killed by boiling, no bugs left alive to infect cold-side equipment).

Below is the process that I followed:
  1. Conduct mash as normal
  2. Remove grains
  3. Boil for 30 mins to sanitize and de-oxygenate the wort (I added 4 IBUs of hops at this stage but most people recommend adding them in the 2nd boil. I was happy for a slower souring on my first attempt and thought it might inhibit some other nasties)
  4. Chill wort to 37 degrees (optimal for Lactobacillus)
  5. Attach CO2 regulator to kettle outlet (regulator is above the level of wort with a one way valve to prevent backflow)
  6. Drop in 700g uncrushed grain (low-kilned malt such as Pilsner) in a large hop bag (or a Lactobacillus culture from Wyeast / White Labs if preferred)
  7. Purge with CO2
  8. Adjust regulator to just barely trickle CO2 through the wort (1 bubble every 10 secs or so)
  9. Place lid back on the urn and cover with glad wrap
  10. Wait 24-36 Hours, monitor temperature and look for the presence of wort in your CO2 line as this may indicate that you are no longer pushing CO2 through the kettle. If so, readjust flow rate.
  11. If the smell is not offensive, taste the wort and allow the process to continue until you are happy with the taste / level of sourness. Beware particularly foul smelling wort as this may not be safe to consume
  12. Skim off the gunk from the top of the wort with a ladle and wipe off the sides of the kettle (these are the more oxygen-exposed, potentially nasty bugs that you don’t want in your brew)
  13. Boil the wort for another 20-30 mins to kill the lactobacillus and any other nasties (add 4 IBUs hops here if you did not do so earlier)
  14. Cool wort, oxygenate and pitch as usual

The one extra step that would further improve this may be to reduce the pH of your wort to 4.5 (to promote Lactobacillus and inhibit other nasties) however not owning a pH meter I did not do this. Next time I plan to add some acidulated malt or lactic acid to achieve this for more reliable results but for this time I let the lactobacillus lower the pH for me =)

Fortunately my BIAB urn setup has two ports which allows me to recirculate through my counterflow chiller. This came in quite handy in the sampling stages as I was able to leave the CO2 at its carefully set rate while taking a sample out of the other port thereby not having to remove the lid and glad wrap (which may allow O2 to enter the head space).

As I brew in the garage it was interesting to see how the smells emanating from the kettle developed. After 24 hours it smelt kind of rancid funky – like someone had put a baby diaper in a bin on the other side of the room – apparent but not overwhelming. After 2 days it had an interesting, not unpleasant funky aroma that reminded me of bailed hay and cattle (without any faecal smells). After 3 days it smelt delicious. It felt like walking into the cellar door of a winery with some wine-like tartness and musty barrel smells.

I ended up stopping the souring process at this stage (68 hours) for this batch. I am particularly happy with the results (tasted like it smelt but a little sweeter) and can’t wait to taste the final product. Below are some step by step images of the process.

Inside of my kettle with whirlpool return from chiller and roasting trivet to keep the bag off the element:
Inside Kettle.jpg

Mash as normal:

Boil and chill:
Boil and Chill.jpg

Sour Kettle after 24 hours:
Sour Kettle 24 hours.jpg

Berliner Weisse after 24 hours:
Berliner Weisse 24 hours.jpg

Sour Kettle after 3 days:
Sour Kettle 3 days.jpg

Berliner Weisse after 3 days:
Berliner Weisse 3 days.jpg

For those interested in the Berliner Weisse recipe I based mine of JZ’s from Brewing Classic Styles. Stats are below:
Pre souring OG = 1.028SG (what BeerSmith told me my pre-boil should be so happy with that)
Other stats are here:

I hope this may provide a template for those of you interested in but daunted by the idea of creating a sour beer. At the least, I hope it provides an entertaining read.

Good luck and happy brewing!!



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Interesting, I just did my first berliner (small batch under 8L) I followed the process from
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