In simple terms, a koelschip—or coolship, as it is more commonly known in America—is a large, shallow steel pan built of either stainless steel or copper that are about a foot deep and are used to both cool down the wort after it is brewed and to spread it out to expose the resulting concoction to naturally occurring yeasts and bacteria that are in the air. The process—otherwise known as spontaneous fermentation—usually takes about 10 hours overnight, and the next morning the cooled wort is then typically transferred into barrels where the fermentation process begins and remains there until the brewery deems it is ready to go on to the next step.

Coolships are most often installed in a high location at a brewery and are typically positioned next to openings like slatted windows in order to allow airflow to have access to the beer. The inoculation process can only take place during cool months of the year to prevent molds that can have undesirable effects on the wort, with a typical desirable temperature averaging about 40 degrees fahrenheit.

This is a traditional method used in Belgium and very few U.S. breweries have the expertise, time or money needed to work with one. While Allagash Brewing Co. in Portland, Maine was one of the first breweries to build one in the U.S. in 2008, there are now multiple breweries around the country that utilize them, including New Glarus Brewing in New Glarus, Wis., de Garde Brewing in Tillamook, Ore. and The Collective Brewing Project in Forth Worth, Texas.

Another company that started using coolships relatively early on—2012 to be exact, after representatives visited Brasserie Cantillon in Brussels, Belgium for the first time—is Jester King Brewery, which is located just outside of Austin, Texas. Its coolship has been installed on the top level of one of the brewery’s barrel aging rooms and is fed through three stain glass windows that run around the room where it is located. In November 2016, the brewery released its first 100 percent spontaneously fermented beer named Jester King 2016 SPON — Méthode Gueuze, a blend of one-, two- and three-year-old 100 percent spontaneously fermented beer.

In this video, Jester King founder Jeffrey Stuffings discusses how the brewery utilizes its coolship to help introduce a “sense of place” into its creations, as the resulting wort is used as the base for many of its beers that incorporate local ingredients sourced not only from around the state of Texas, but also around the physical location of the brewery itself.