What the Heck Is a Kettle Sour Berliner Weisse? Celebrating Our First Sour Beer

Our recent expansion to 16 taps has made it a lot easier for us to experiment with new beer styles. Maybe you’ve tried our new Alt, Belgian Tripel, or enjoyed a pint of Schottky Pumpkin on nitro, none of which would have been available had we not been able to double our on tap offerings. But no style has been asked about more than the style we just released last week: a sour beer.

A tulip packing a ton of pucker power.

Sours are tricky. To create a traditional sour, you take already fermented beer and introduce wild yeast and/or bacteria to referment the beer, often times in an oak barrel or occasionally in a stainless steel tank. This process can take months to years, and also can create a contamination risk for your other beers and equipment.

Instead, we settled on a method called kettle souring. In making a kettle sour, we brew everything normally up to the boil process, when we transfer it to the boil kettle for a quick 10 minute boil to sterilize the wort, then dose it with lactobacillus (one of the most common souring agents, commonly found in yogurt, sourdough bread, and more) and seal it up in the boil kettle to sour (hence “kettle” souring). Over the course of 1-3 days, the lactobacillus consumes some of the sugars extracted from the malts earlier in the brewing process and converts them to lactic acid, which lowers the pH of the beer, giving it a sour flavor.

A layer of pellicle, a biofilm biproduct of the lactobacillus souring our wort, as shot through our sealed boil kettle cover.

Once the wort has our desired level of sourness and hits the pH we were aiming for (3.4), we add our hops and get everything boiling again to kill all the lactobacillus and halt all the souring. Because all of this is done in one vessel and then immediately boiled in that same vessel, it’s a substantially safer method of souring beer with much lower contamination risks. From here, the beer gets a pitch of brewers yeast and ferments just like normal. Faster and safer for a brewery of our size is a no brainer.

The soured, and now boiled, wort. Ready to be transferred and fermented with standard brewer's yeast.

So what kind of sour did we make? We brewed a Berliner Weisse, a traditional German sour ale that uses a blend of wheat and barley (in our case, pilsner malt), creating a beer that’s light in both body and color and allowing the tart flavors to shine through. Because some of the sugars extracted from the malts are consumed by the lactobacillus before the brewer’s yeast can convert them to alcohol, Berliner Weisse also have relatively low ABVs (2.8-4%) compared to standard beer styles, meaning it’s incredibly easy to have a few in one night.

Traditionally, Berliner Weisses were also combined with raspberry or woodruff syrups to help balance the tartness. American craft brewers have expanded this to include fruit syrups or even fresh fruit purees. Our initial take on the style was aged on passionfruit puree, which has a pleasant balance of sweet and tart fruit notes and pairs perfectly with the tartness of the Berliner Weisse.

Our finished product, the first sour we've ever made.

We also kept 10 kegs of our first Berliner Weisse separate from the passionfruit and will use these to create some experimental sour ales featuring completely different flavors. Got an idea for what you’d like to see featured? Let us know!