How to Make a Kettle Sour Beer

How To Make a Kettle Sour Beer

What is a Sour Beer?

Sour beers are usually made by introducing wild yeast or bacteria to already fermented beer via barrels or by cooling finished wort in vessels called coolships.  Hot wort goes into the coolship to, well, cool. While cooling the wort is naturally inoculated with wild yeast/bacteria floating around in the air. Oftentimes coolships reside in the attics of old-style breweries where windows are opened to produce air flow and encourage spontaneous fermentation.

However, these methods have some drawbacks. First, results can often be inconsistent. By introducing wild yeast and bacteria via open air circulation you’re at the mercy of nature. If the “wrong” wild yeast and bacteria are introduced to your wort, or if they’re introduced in the wrong proportions, the souring process will be less than optimal. Further, these souring methods are incredibly time-consuming. The total process can often take up to 24 months (yes, you read that right, MONTHS). This is obviously a long time to wait, and brewers are a thirsty lot. Good thing they’re also inventive. Enter the world of kettle souring.

What Is Kettle Souring?

Kettle souring, unlike the traditional souring methods, can sour unfermented wort incredibly rapidly. In fact, if the conditions are right, the entire souring process can take as little as 24 hours. Best of all kettle souring is relatively simple to make.

How to Make a Kettle Sour

1. To begin, create a wort just as you would normally. That is to say, if you want a sour pale ale, make a wort that would make a great pale ale. If you want a sour stout, brew a wort that would make a great stout. After brewing the wort, boil it for 10-15 minutes to sterilize it. Note: You are only creating the wort at this point, the full boil with hop additions will come later in the process.

2. Cool the wort to 75 - 95 degrees F (24 - 35 C) in the kettle.

3. Keeping the wort in the kettle, add a strain of pure lactobacillus to your cooled wort.

  1. For optimal performance, the lacto culture should be kept at ~90 degrees F.  A great way to maintain this temperature is by using a temperature controller kit.

4. Once introduced, the lactobacillus, or “Lacto”  will go to work and begin consuming sugars in the wort transforming them into lactic acid. The lactic acid creates the tart flavor we know and love in sour beers. Allow the lacto to do it’s thing for 1 to 3 days.

  1. A pH meter is recommended to determine when the kettle souring process is complete. For a light sour flavor, target a pH in the mid to upper 3s. If you want an eye-watering sourness, shoot for a pH in the lower 3s.
  2. If you don’t have a pH meter, draw a small sample of the wort with a sanitized utensil and taste. When the beer has reached the desired level of sourness you can begin the boil. Remember, there is still a lot of sugar present in the wort at this point, those sugars will disguise the true sourness of the wort (think adding sugar to overly sour lemonade). So don’t overdo it.

5. Once you have reached your desired sourness you can pick up right where you left off. Place your kettle back on your burner and pick up your boil where you left off.

6. Complete your recipe exactly as you would otherwise.

That's it, kettle souring complete. Once your beer completes normal fermentation it will be a sour, no need to wait 2 years to enjoy.