Making Kettle Sours

It took a while for brewers outside of the small sour brewing centers of Belgium and Germany to produce excellent sours because so much of the science and practice of sour beer brewing was closely guarded ~30 years ago when brewers from other parts of the brewing world began dabbling with sour beer. Jean-Xavier Guinard’s Lambic (Brewer’s Publications, 1990) was really ahead of its time because there were very few U.S. homebrewers, let alone U.S. microbreweries, that were experimenting with sour beers in 1990.

In retrospect, it is pretty amazing that JX, as he was known by his colleagues at UC-Davis, was actually brewing sour beers in the UC-Davis brewing lab while completing his Ph.D. because Dr. Michael Lewis was not a big fan of contaminated beer. I remember having a conversation with Dr. Lewis sometime in 1992. We were sitting in his office when the phone rang. I could only hear one side of the conversation, but the topic was clear; a well-known microbrewery was interested in brewing Berliner Weisse. Dr. Lewis repeatedly asked the brewmaster on the other end of the line “why do you want to [mess] up your brewery by bringing Lactobacilli into your cellar?” I don’t know if Dr. Lewis’ continual protests influenced this brewer, but the brewery never produced a Berliner Weisse. But in the brewing lab, a small collection of JX’s lambics remained in storage for the occasional tasting. I don’t know if those beers were as excellent as I remember them being, but they seemed like the real deal at the time. It was like JX transported the magic from Belgium to Davis using that clichéd blend of art and science.

The early sours to hit the US microbrewing scene were brewed in the Belgian tradition. New Belgium launched La Folie in 1997, Tomme Arthur was brewing sours at Pizza Port in Solano Beach, California in the late 90s, Vinnie Cilurzo was busy up in Santa Rosa, California in the early 2000s and Tim Schwartz was brewing some great sours in Austin, Texas at the Bitter End in the late 90s and early 2000s. Today there are breweries in nearly every state with sour barrel programs. Although many of these beers are produced in less than a year, sour barrel programs require a substantial investment in beer, wood, and space. There is also a higher level of risk with these beers and many breweries simply steer clear of sours that develop in the cellar.

I am not sure when US brewers began producing any real volume of Berliner Weisse-type beers, and their Gose-inspired cousins, but it was really only after the early Belgian styles were garnering attention in the beer world. Indeed, some of the brewers playing with sour barrels were also playing around with bacteria in the brewhouse. Although traditional Berliner Weisse is fermented with a mixed culture of yeast and bacteria, and bottled with the same, modern interpretations can be produced in the brewhouse to keep their fermenters clean of bugs.

With the growth of this market segment, the supplies required to produce these beers has also grown. The various bacteria and yeast used to brew these beers have gone from obscure and guarded to readily available from brewing yeast suppliers. Most of the cultures used to sour beer in barrels are mixed, whereas the bacteria used for kettle sours tend to be single strains, or a mixture of Lactobacillus species. Some brewers use yogurt as the source for bacteria, but this can be hit or miss.

The most common methods use the brewhouse to produce sterile, very lightly hopped wort. Start with a normal boil or by holding wort at near-boiling temperatures for 20-30 minutes, effectively pasteurizing the wort. Next use a wort cooler to temper the wort into the 95-122 °F (35-50 °C) range, hit it with carbon dioxide to strip oxygen from the wort and to try to maintain an anaerobic environment. Then add the bacterial culture to get the party started. Most kettle sours only require about 48 hours for the wort to sour, and the progress of souring is usually monitored by pH or titratable acidity (TA).

When the process is complete, the sour wort is boiled, cooled, aerated, and pitched with yeast. The beauty of this method is that it keeps the bugs out of the cellar, and only adds a couple of days to the normal brewing process. Since this technique is easiest carried out in the brew kettle, it does have the disadvantage of tying up the kettle and greatly reducing brewhouse utilization. Many breweries have worked around this dilemma by adding sour wort tanks to their brewhouses.

If you are new to kettle sours, do yourself a favor and simply buy a pitchable culture. Growing these bacteria is a bit different from growing yeast because the acid production can suppress cell growth. If you want to propagate your own cultures, consider using a carbonate buffer in the propagation media to keep the pH in check. Milk the Funk has some great practical advice on their website regarding techniques to best grow these bugs.

While the kettle sour method produces very clean, and sometimes very sour beers, the beers are often criticized by lovers of Belgian sours for being one-dimensional. This is where fruits, herbs, spices, and other beers enter the equation. If you have a great sour base, use it like vinegar in your kitchen and blend with other ingredients. These ingredients can be added at any step of the process depending on what makes the most sense. And this is how many of the new generation sours are being produced and are key to their success.

Although some folks really like things that are simply sour, most like sour foods and beverages that are balanced by sweet, salty, or hot ingredients. This is where blending can transform one-dimensional kettle sours into a wide array of new and interesting flavor combinations. Sweetness can come in the form of a neutral beer, like a wheat beer, to smooth out acidity and add a little body and texture to beers that can come across as very dry and thin. Fruit juices add sweetness, fruitiness, and aromas. Fruit essences, such as citrus peel oil, can be used to add top notes. Herbs and spices can also be used to add aroma and complex flavors. And the judicious use of salt and heat may be fun to bring into the mix for certain flavor combinations. These sorts of methods are being used to produce some of the new generation kettle sours that are popping up on the shelves with price tags that are more in-line with IPA. I hope this helps you ease your foot into the sour end of the pool!

Response by Ashton Lewis.