Kettle Souring Beer – Brewing Techniques

by Brad Smith on October 8, 2017 · 4 comments

This week I take a look at “Kettle Souring” beer which is a technique for making sour beer that offers faster fermentation times and better control over the souring levels.

The Kettle Souring Method

The traditional method for making sour beer is to brew some wort and then pitch both traditional brewing yeast along with some form of live bacteria to slowly sour the beer. The bacteria will produce lactic acid which gives the beer its distinctive sour flavor. This method typically takes several months or more to ferment and age properly as the infected beer often develops some off flavors that take time to settle out and fade before drinking.

As I mentioned in an earlier article on Berliner Weisse, kettle souring offers an attractive alternative. You prepare your wort just as you would for a traditional fermentation, and then pitch only bacteria (typically Lactobacillus or Pediococcus) to begin the souring process. Once you reach the desired level of sourness and pH, you then boil the soured wort to kill off any remaining bacteria.

At this point you can either continue fermenting by pitching fresh yeast or alternately blend the soured wort with fresh wort from another batch to ferment a blended beer. The beer will typically ferment and finish quite quickly if the pH is not too low, giving you a nice clean sour beer in a matter of weeks instead of taking many months. If you are making a very sour beer, I do recommend monitoring the pH as it can drop during fermentation. I like to keep the pH above 3.0 at a minimum, as fermentation can be slowed or even halted below that level.

Advantages of Kettle Souring over Other Souring Techniques

I mentioned that kettle souring is much quicker to complete fermentation than a traditional sour fermentation method, and also results in a cleaner overall sour flavor profile. It also has a substantial advantage as you can manage both the pH levels and level of sourness during the souring stage and cut it off by boiling when you reach the desired level of sourness. Also if you use the option to blend sour wort with fresh wort you can even more precisely control sourness.

Another technique known as mash souring involves actually leaving the mash out in open air (or innoculating with bacteria) for one or more days to sour the mash before proceeding with lautering, boiling and fermentation. Unfortunately this technique also results in more funky off flavors than kettle souring, so again kettle souring wins as far as souring techniques.

I will mention that since kettle souring gives you a cleaner sour finish, it might not be ideal for beers where you are truly looking for funky sour complexity such as a traditional lambic. So if you want a lot of funk you might want go proceed with a more traditional sour fermentation and give it the months or years needed to reach maturity.

I hope you enjoyed this article on kettle souring. If you have your own thoughts on sour beer techniques please leave a comment below. Thanks for joining me on the BeerSmith Home Brewing Blog. Be sure to sign up for my newsletter or my podcast (also on itunes…and youtube…and streaming radio station) for more great tips on homebrewing. Also check out the How to Brew Video series I shot with John Palmer if you want to learn more about all grain brewing.

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{ 3 comments… read them below or add one }

Kevin Dufresne October 10, 2017 at 11:43 am

Hi Brad,

Is it better to increase a little bit the temperature while adding the bacteria to make it more efficient?
Also is it neccessiry to add Co2 while waiting to avoid oxidation?


Jonathan Coulombe July 22, 2019 at 7:49 pm


If I Mash in aluminium, is it ok to sour the beer in that vessel or do I need to transfer in stainless or glass?


sbrewing company November 21, 2023 at 3:09 am

Thank you for sharing! The Kettle Sour Beer Brewing Technology blog provides valuable insight into the complex process. The detailed instructions and user-friendly approach make it an invaluable resource for both beginners and experienced brewers looking to master this innovative brewing method.

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