Nothing is cooler than coolships — especially for retro-futurists who love great beer.

A large, shallow vessel made of copper or stainless steel, coolships are used to cool wort so it can spontaneously ferment into beer. They have been used for centuries, most famously for Belgian lambic at revered breweries like Cantillon. (The rad-sounding term “coolship” comes from the Flemish koelschip.)

The use of coolships was mostly abandoned after refrigeration and temperature-controlled equipment like heat exchanges and cone-shaped fermentation tanks came into play.

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In the last decade, however, coolships have experienced a small renaissance among American craft brewers, with brands like Allagash, New Glarus, Russian River, Jester King, Black Project, and The Veil adopting the practice to make a variety of lambic-inspired, spontaneously fermented sour beers.

Coolship Fermentation: A Wild Party

Coolships vary in size and depth, but they are typically large, rectangular, shallow vessels that take up the span of a room and lie open to the elements. This allows several things to happen. The high surface area allows the liquid to cool as quickly as possible (most brewers let it cool overnight). It lets any brewing material left in the wort, called trub, to settle out.

Perhaps most importantly for brewers using this method to create sour beers, the uncovered vessel is able to pick up airborne yeast and microflora that will inoculate the wort and give beer its funky or sour flavor once it is fermented. In other words, “wild” bacteria and yeast floating in the air jump in the pool and have a party. The vibe of the party depends on things like the time, place, and season — this creates a wild beer’s unique terroir.

It’s called “spontaneous” fermentation because microbes come at random, rather than a brewery using specific strains of yeast developed in a lab.


It’s All Thanks to Cantillon

Centuries ago, coolships were the norm. In medieval times, brewers used a hollowed-out tree trunk similar to a boat. (This may be where the “ship” concept comes from.)

The most famous coolship is that at Brasserie Cantillon, a world-renowned lambic producer in Brussels, Belgium. Cantillon has been producing beers in the lambic tradition since 1900. American brewers inspired by Cantillon have now set their own coolships asail, with at least two dozen coolships in use in the U.S. today.

Coolships today are most often located in an enclosed room with vents or windows that allow air (and its microbes) to flow in. There are some exceptions — one extreme example is when Arizona Wilderness Brewing hosted a camping retreat in 2016 called #campcoolship, bringing 15 brewers and a mobile coolship into the mountains.

Craft Brewers Keeping Coolships Cool

Inspired by a visit to Cantillon, Allagash Brewing installed a coolship in 2007. The beer from those original batches still comprises the base beer for current brands in its Coolship series like Coolship Resurgam, Coolship Red, Coolship Cerise, and Coolship Balaton.

Dozens of breweries followed suit. In 2012, Russian River Brewing began using a coolship for beers such as its Sonambic and Beatification. Jester King Brewery in Austin, Texas, and Side Project Brewing in St. Louis, Mo., began using coolships at their breweries in 2013. New Glarus installed its coolship in 2014.


The Veil Brewing in Richmond, Va., opened in 2016 and got its name from coolship fermentation. That yeast party we mentioned? After a long night at a coolship party, a layer of organic matter forms on the surface of the wort, called “pellicles.” When brewery co-founder and head brewer Matt Tarpey apprenticed with Cantillon owner and brewer Jean Van Roy, he learned that winemakers refer to this layer as “the veil.”

With more brewers than ever adopting this ancient method, and adjacent practices like the solera method, American wild ales are creating whole new worlds.