Coolship Fermentation: The Wild Side of Brewing


Before anyone knew the science behind how beer was made, brewers used a coolship (koelschip in the original Dutch) to chill the wort using the ambient air.

The typically wide and shallow container provided enough surface area for the wort to cool. However, unbeknownst to the brewers at the time, it also allowed area yeast and bacteria to find their way into the beer. The end result was a sometimes delicious, always unpredictable finished product as different outside elements made it into the batch each time.

Modern brewers have a much better understanding of both yeast and the importance of quickly cooling a beer to the proper yeast pitching temperature in order to limit the addition of random funk into the batch.

If you’re into that sort of thing.

We’re not.

When Wild Mind opened in late Summer 2016, finding a way to bring back the coolship and the funky, unpredictable beers was one of the first priorities. We tend to focus on brewing traditional farmhouse-style beers, and the coolship is the epitome of paying homage to old world brewing techniques.

There’s a lost art to harnessing the unpredictability of a coolship. As a bonus, coolship brew days are the absolute BEST. DAMN. DAYS. If you’ve ever walked into the brewery and thought it smelled amazing, it’s more than likely the coolship was the culprit. Take a peek through the glass as you walk through the front door, and you might just see it in action.


Our coolship, the first one in Minnesota for spontaneous fermentation in the lambic style of brewing, was crafted by a local fabrication company after Head Brewer Mat Waddell researched wort cooling rates, inoculation rates, and what surface area would be needed for a 10 bbl coolship.

Each coolship batch is completely a new style. Many of our coolship beers are 100 percent spontaneously fermented, but we also have open-fermented coolship beer and are continuing experimenting with each new batch. While most coolship beers take anywhere from 1 to 3 years to reach your glass, we put some of our coolship beer into mature wine barrels to help speed up the process.

We brewed our first coolship beer during the first week of October in 2016. For our first attempt, we decided to stick to the tried-and-true lambic style. True to style, we used a turbid mash, included aged hops that were more than two years old, and boiled the wort an extra long time.

The end result is a thing of beauty. The calculated randomness of the coolship means each beer will pick up flavors you can’t get anywhere else.

The coolship might come out to the courtyard to pick up some new flavors. It could find it’s way to the roof. Or who knows, maybe we’ll put it on a flatbed and idle around the neighborhood — capturing all the funk of South Minneapolis.