Making a Kettle Sour with Lacto Cultures

Category : Technical
Date : March 7, 2021
Author : White Labs Technical Team

Making a Kettle Sour with Lacto Cultures

Kettle souring can be a convenient method for creating a crisp, clean, tart beer. Using a Lactobacillus culture pre-fermentation allows you to ferment wort at a higher temperature for quick acid production. 
Pitch Rate Calculator

Not All Strains are Alike 

Each Lactobacillus species is not created equal. Most of the species that have been used traditionally have been isolated from grain, but more recently, cultures used for creating yogurt have also become popular. Each of these strains has different conditions they like and different flavors and aromas they make. White Labs provides 2 different species year-round for your kettle sour needs.

WLP672  Lactobacillus brevis
WLP677 Lactobacillus delbrueckii


Pitching Rates 

Like Brewer’s yeast, the more cells in the fermentation, the faster the souring process will go. We recommend 1.2L of our Lactobacillus cultures per 5BBLs of wort or 0.35L/ 1HL of wort. This will typically provide a large pH drop within 24 hours and a maximum drop within 48 hours at the strain's optimal temperatures.  


Here is an example pH drop from our recommended pitch rate of 1L of our Lactobacillus cultures per 5BBLs of wort. See how different strains strive at different temperatures.

Troubleshooting Off-flavors 

When wort is fermented with lacto and >100°F, the potential for food pathogens arises. It’s important that the wort is clean and the pH starts dropping quickly. If some unwanted organisms arise, one of the classic off-flavors, butyric acid, can be present. The smell of baby vomit is almost impossible to get rid of or blend out so avoiding it in the first place is the best practice. All of these organisms would be killed after the boil, but starting with a pre-acidified wort can help prevent this from occurring. 


Blending is key

Different Lactobacillus sp. range from the amount of perceived sourness they produce. Depending on how they are treated, some produce more lactic acid than others, where lactic acid can have a harsher note of sourness. To combat this, we recommend blending different Lactobacillus strains as well as other acid-producing strains to create a more complex and rounded acid profile.