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Souring with Lactobacillus: Tips from the Pros

Soured beer can be produced in the same amount of time as non-soured styles with the help of Lactobacillus. Generally, this is done using the kettle-souring method for styles like Gose and Berliner weisse, however other methods and styles are sometimes in play too. Three pros share some sweet tips on souring with Lacto

Fal Allen, Brewmaster at Anderson Valley Brewing Co. in Boonville, California.

At Anderson Valley we have about eight years of kettle souring experience. We use this method for making our Goses and, on occasion, other beers (like our Tropical Hazy Sour beer). We also do a fair amount of barrel souring beers — we have about 1,200 wood barrels in our sour beer production. This process differs greatly from the kettle souring process. It can take anywhere from nine months to four years to sour a beer this way; in contrast kettle souring can be done in less than 8 hours. The flavor that each process creates can be very different as well. We use kettle souring to create clean, sharp, bright tartness and we use our barrel souring process to create a more complex, deeper, funkier range of flavors. For kettle sours, we keep our temperature at about 108–112 °F (42–44 °C). We use a strain of Lactobacillus delbrueckii that seems to work best at that temperature, but each strain is different. 

We have tried several sources for Lacto, but we prefer the one we get from a lab. It creates flavors we like, and it creates these flavors more consistently on a regular basis. It is also healthier than some other sources, which makes it easier to grow up to the proper pitching rate. 

Prior to pitching the Lacto we look for the same pH as we would in any of our other beers (about 5.2). We do a very large pitch of lactic acid bacteria (LAB) and expect to see the pH drop in to our desired range within 6–8 hours. We also exclude oxygen from the process as much as possible and this helps retard unwanted bacteria with no deleterious effects on the LAB. We do not add extraneous acid to our kettle souring process other than to adjust the pH of the brewing water prior to mash-in (which we do for all our beers as our water is quite high in pH).

After the Lacto does its thing we prefer a wort pH of 3.35 to 3.25, but will accept wort between 3.4 and 3.2. We are looking for a clean, bright acidity and don’t want the pH to be less than 3.2 or above 3.4. We also use titratable acidity to judge acidity and its quality of impact. Future fruit additions play into our target sourness level to a lesser extent. We are trying to achieve a harmonious balance of flavors and if a fruit has a very low pH we will factor that into our kettle souring process. 

Other important factors for kettle souring is to get the wort off the grain (as you would with a “normal” beer) and into the kettle. This needs be done to avoid too much bad funkiness that you would probably get in your wort if you did not sour it fast enough. The second thing is sour your wort fast (in less than 24 hours). To achieve that you need to pitch a good amount of LAB into the kettle; slightly more than one million cells per mL per degree Plato. So about 12 million cells per mL for a 11 or 12 degree Plato wort (1.044–1.048 specific gravity).  And the third thing is to exclude oxygen as much as you can.  This will help keep the bad funk in check. We blanket the top of the kettle with an inert gas to help keep oxygen out of the process. 

For much more on the subject, I wrote the book on Gose for the Brewer’s Association’s style guideline series and there is a lot of information about kettle souring in there.

Nicole Reiman (right), Head Brewer & Amanda Oberbroeckling (left) Head of the quality control lab at Odd13 Brewing in Lafayette, Colorado

At Odd13 we’ve been kettle souring for about five years. We employ this method any time we produce a sour with the intention of canning. The kettle souring method is perfect for our process because it provides us with a finished product that maintains the same flavor through the shelf life of the beer. Conversely, we use traditional souring methods with small experimental batches. Most of these are long-term souring processes, typically using Lactobacillus and Pediococcus and aging in barrels or foeders. We have also experimented with open fermentation in foeders.

We get our Lacto from Inland Island Yeast Laboratories, out of Denver, Colorado. We prefer L. delbrueckii because it gives us a quicker sour, keeping the wort at 115 °F (46 °C). In the past we have also worked with several other Lacto species at various temperatures, including L. brevis, and have found that at incorrect temperatures there is either less activity or too much activity. We chose our current temperature based on the recommendation from our supplier.

Our process across all of our production is to acidify our wort to a pH of 5.2 using lactic acid. Then, after the souring phase, we typically target a pH around 3.5; however, the decision to stop the souring process is ultimately determined from sensory evaluation of the wort. As we expand our portfolio to include more fruited sours we do take into consideration the acidity level of the fruit that will be added to the beer, and adjust the target pH accordingly. This typically results in a higher pH wort so that fruit additions don’t turn the beer too sour.

The most important lesson we’ve learned is that kettle souring is its own process that requires great attention to detail, and has its own intricacies that don’t necessarily carry over from traditional brewing methods. The kettle souring process introduces the possibility of less common off flavors, such as isovaleric acid and butyric acid. We’ve learned that it’s important to make sure the process is dialed in — do your homework and come up with a plan before just jumping in. Monitor and control the process, including cleanliness, wort temperature and pH, and gas levels . . . oxygen makes Lacto angry!

Joe Mashburn, Head Brewer at Night Shift Brewing in Everett, Massachusetts

We don’t kettle sour, but rather have a Lactobacillus fermentation phase, followed by a brewer’s yeast fermentation for our Weisse Series releases. We’ve done a single kettle sour and weren’t happy with it, so we moved on from that. Now, we never denature the Lacto and really like the consistency and results of this approach. We produce between 200–300 bbls (6,200–9,300 gallons/235–352 hL) of this style each month. We’ve also used Lacto for more time-intensive Lacto/Brettanomyces/brewer’s yeast fermentations, which are generally destined for oak barrels that will have adequate time for the Lacto to produce acid and the Brett to do its thing. 

For our Weisse Series beers, we target a pH of 5.2 in the kettle, just from normal mashing/sparging procedures. We haven’t played around with acidifying prior to Lacto additions, mostly because the 5.2 gives us the results we’re looking for. 

We use a Lacto culture from Lallemand, but we’ve also tried White Labs and Brewing Science Institute. The Lacto from Lallemand is incredibly easy to use and it comes as a dry pitch so it has a very long shelf life. For that addition we knock out at 100 ˚F (38 °C). This has been the same for the two different types of Lacto we’ve tried. When the pH reaches 3.2–3.3 we then pitch the brewer’s yeast. Our sours are heavily fruited, so that low of a pH helps the acid come through.

When working with Lacto, watch your diacetyl production. We’ve had success eliminating and minimizing diacetyl by adding fruit early in fermentation (day 2). Additionally, during the Lacto fermentation, try to eliminate all oxygen. You could hook up CO2 to an oxygen stone and continue to purge during knockout. If you don’t have an oxygen stone, try not to splash during knockout.