Home Behind The BeerSource of Style Source of Styles #17 : Kettle & Sour Beers

Source of Styles #17 : Kettle & Sour Beers

by BeerTengoku Writer
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We’re slowly approaching the legal drinking age in terms of entries into our “source of styles” and for this one, we’re going to look at sours and kettle sours – both a style and also a method of making beer. Kettle sours are a polarising type of beer – drinkers both love the immediacy of the style that traditional sours lack, but drinkers also lament the lack of complexity that traditional sour beers have. Our suggestion? Have the best of both worlds and appreciate the advantages that both styles have to offer.

When we talk about kettle sour beers, we’re not talking about beers that have soured either due to poor brewing techniques or due to age. Rather, we’re looking at beers that have been deliberately soured in a controlled manner. The great American painter Bob Ross may have used the phrase “a happy little accident” but these beers are no longer the happy little accidents that they once were, with brewers controlling the steps very carefully along the way.

Kettle sours differ from the traditional sense in that the brewing process is faster, often much faster than the traditional method, as employed in beers produced by esteemed breweries such as Cantillon and Boon. However, those beers are known to take months, if not years, to reach their prime condition, with kettle sours reaching their prime within a few weeks.

A Brief History of Sours

While the process of brewing beer had been around for years, essentially all beer that was made before pasteurization and refrigeration had the potential to be a sour beer. Unless brewers had an impeccable level of cleaning and sanitation in their equipment, naturally occurring bacteria in the air could be found around a brewery, with the ability to spoil a beer. With developments of yeast growing and selection of strains, in the 1800s, brewers were able to exclude bacteria, like lactobacillus, that gave off undesirable flavors.


However, European brewers, in particular those in Belgium and the Flanders region, were deliberately exposing their beer to wild yeast, and using bacteria such as lactobacillus and  brettanomyces, amongst other wild bacteria, to provide flavour profiles that normal yeast was unable to produce. 

The process of producing a traditional sour is rather simplistic and, in spite of the innovations and techniques that have changed brewing, remains the same to this day. In the case of Cantillon, brewing only takes place during the cooler months of the year, usually in winter time, as the fluctuations in temperature remain low, as does humidity level. During these months, each batch of beer is pumped directly from the boil kettle into what is known as a coolship, or koelschip. This is a huge metal pan, often quite shallow, and is uncovered, thus exposing it to the air. The brewers will then open louvered vents and turn on the fans, encouraging the air to flow over the koelschips, which contains wild yeast in the area, along with bacteria. While this sounds like a random method of brewing a beer, the region around the Cantillon brewery hasn’t changed and the building that holds the brewery also has its own in-house yeast – literally coming from the wooden rafters in the roof. Once the wort has cooled down, and been inoculated with the wild yeast and bacteria, it is then pumped down into empty Burgundy barrels, for up to four years, and later be blended and re-fermented, sometimes with locally sourced fruit, to make varieties such as Cantillon Kriek (cherry), Rosé de Gambrinus (raspberry), and Fou’ Foune (apricot). 

Kettle sours are an increasingly popular form of the style of beer, with the immediacy and turn around offered by them allowing breweries to produce a beer that requires less effort, both in terms of care of the beer and making space for a beer that can take months, or even years, to make.

Lactobacillus though still has an integral part in making a kettle sour, with it being introduced deliberately by the brewer at a set point in the brewing process. In a traditional sour, the wort is left outside to chill, but in a kettle sour, rather than boiling the wort and then cooling it outside to ready it for yeast, the liquid is boiled, cooled, and lactobacillus is then added. This wort mixture then chills for a few days in the “kettle” while the liquid sours. Once the desired level of tartness is achieved, measured by the pH of the beer, the normal brewing process is resumed. Boil; add hops; cool wort; add yeast and let ferment. The beer is soured in a stainless steel mash tun and fermented in a similar tank. Here in lies one of the key differences between kettle sours and traditional sours: steel over barrel.

Kettle sours lack the complexity of traditional sours due to the usage of stainless steel and its permeability to the outside. Any equipment that has come into contact with lactobacillus, or the wort, needs to be thoroughly cleaned, else it may affect other beers that are made in the brewery. The brewers scrub away the residual flavours left by the kettle-soured wort, which thus lacks the complexity of traditional sour beers.

Sours Appearance and Taste

Due to the wide ranging nature of sours, and kettle sours, the BJCP are also wide and varied too. The key point to remember is that these beers have been deliberately designed to be sour. If you have an IPA that is sour, and it was unintentional, then you’re drinking a bad beer.

Appearance: Variable by base style. Clarity can be variable; some haze is not a fault. Head retention can be poor due to high levels of acid or anti-foam properties of some lactobacillus strains.

Aroma: Variable by base style. The contribution of non-Saccharomyces microbes should be noticeable to strong, and often contribute a sour and/or funky, wild note. The best examples will display a range of aromatics, rather than a single dominant character. The aroma should be inviting, not harsh or unpleasant.

Flavor: Variable by base style. Look for an agreeable balance between the base beer and the fermentation character. A range of results is possible from fairly high acidity/funk to a subtle, pleasant, harmonious beer. The best examples are pleasurable to drink with the esters and phenols complementing the malt and/or hops. The wild character can be prominent, but does not need to be dominating in a style with an otherwise strong malt/hop profile. Acidity should be firm yet enjoyable, but should not be biting or vinegary; prominent or objectionable/offensive acetic acid is a fault. Bitterness tends to be low, especially as sourness increases.

Characteristic Ingredients: Virtually any style of beer. Usually fermented by Lactobacillus and/or Pediococcus, often in conjunction with Saccharomyces and/or Brettanomyces. Can also be a blend of styles. Wood or barrel aging is very common, but not required.

Japanese Sour Beers We Recommend

Daisen G Beer Amabie

Shiga Kogen Barrel Aged Yamabushi Red

Songbird Fuji

Songbird Manos Verde

Japanese Kettle Sour Beers We Recommend

TDM 1874 Sour Marionberry

Kyoto Indigo Skies

West Coast Black Market Trader

Imported Sours We Recommend

Let’s be honest – if you’re going to try a style of beer, then it’s also worth trying out some of the overseas beers. With the massive influx of beer, both Belgian and American, it should be quite easy to find some of these beers on here, while others are much harder to find. Check out the label on the bottle to see when the beer was bottled, and also ask how the beer was imported. Was it in a cold chain from start to finish? Was the beer stored in a chilled environment in store? If the shop assistant can’t, or doesn’t know the answer, then give it a miss.

Rodenbach Grand Cru (Belgium)

Cantillon (Belgium)

Crooked Stave Artisan Beer Project (USA)

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