Sour Beer Alternatives for Home Brewers – Part 1: Kettle Souring

by Brad Smith on March 9, 2022 · 0 comments

This week I’m going to cover the two major methods (in two parts) used to create sour beers at a home brew level. While sour beer brewing is considered a more advanced brewing technique, it is possible for even a beginning homebrewer to create great sour beers using these methods.

Sour Beer Basics

Sour beers have been around for the entirety of beer history. The sour flavor comes from lactic acid which is primarily a byproduct of infection by bacteria, though we are now also finding out that some wild yeasts can produce lactic acid also. Before the discovery of yeast by Pasteur in 1857, wild yeast was widely used to ferment beer so most historical beers were in fact likely slightly on the sour side. Lactic acid drives the pH of the beer down giving a sour finish to complement the sour flavors.

Even before the discovery of yeast, breweries often reused yeast slurry from one batch to another eventually cultivating brewing yeast. Today we are fortunate to have access to a wide variety of extremely pure brewing yeast, but also a selection of cultured bacteria including lactobacillus and pediococcus. Lactobacillus is the more commonly used variant as it adds sourness without a lot of off flavors. It is not very hop tolerant, and sometimes lowers the pH so rapidly it can produce off flavors.

Pediococcus acts more slowly than lactobacillus, is more hop tolerant and can also drive the pH below 3.0 for more sour flavor. However Pedio also produces diacetyl (a buttery popcorn) off flavor. Often Pediococcus is used in combination with Brettanomyces (a specific yeast strain) which converts some of the diacetyl to other compounds and adds a bit of its own funky flavor.

Equipment Considerations

One concern with working with bacteria is that they can easily infect plastic and rubber, so much so that many sour beer brewers maintain separate sets of equipment for sour and non-sour beers on the cold side (i.e. post-boil). I personally do not recommend mixing any plastic or rubber equipment that comes in contact with the wort once you have pitched your bacteria. This includes little things like plastic transfer hoses and rubber or plastic seals on your fermenter or pumps.

Two Beer Souring Options

There are two main options when it comes to sour beer techniques. The first, called “kettle souring” is done by adding the bacteria up front before the main fermentation and souring before you ferment. The second, traditional method is to ferment the beer first with regular yeast and then add the bacteria in the secondary.

The kettle souring option has the advantage of speed as the souring can be done quickly, and you can monitor the pH level to get the desired amount of sourness before killing off the bacteria (usually by boiling again) and pitching your regular yeast. However, kettle souring can produce some off flavors due tot the rapidity at which the bacteria work giving an entirely different flavor profile.

Traditional souring gives a more aged, blended finish to the beer, but takes considerable more time. Since most of the sugars are consumed in the initial yeast fermentation, it can take months to complete a traditional sour fermentation.

Kettle Souring Basics

  • Mash and sparge as you normally would using a simple infusion mash. If you are an extract brewer, you can start with the boil as you normally would.
  • Boil for your normal period of time, but don’t add the hops yet. Hops will inhibit the bacteria so you will actually add your hops during a second boil later.
  • Some sources recommend lowering the pH to 4.5 at this point using lactic acid to reduce the chance of infection.
  • Cool the wort and start fermentation with lactobacillus. Allow it to ferment for a few days keeping it warm (ideally in the 100+ F or 43 C+ range.
  • You can monitor the pH and once it reaches 3.6-3.8 typically you will cut off fermentation.
  • Transfer the wort back tot he boiler and add your normal hops while boiling. Boiling the wort will kill off the lactobacillus.
  • Cool the wort again and pitch your regular brewing yeast. Then ferment and finish the beer as you normally would.

That is a quick summary of the kettle souring method. Next week in part 2 I will cover the traditional method for making sour beers.

I hope you enjoyed this week’s article from the BeerSmith Home Brewing Blog. Please subscribe for regular weekly delivery, and don’t hesitate to leave a comment or send this article to a friend.

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