Spontaneously fermented beers from Portland breweries Rising Tide, Allagash and Liquid Riot. Photo by Caitlin Enz

While coolship beers are most closely associated with Belgium, Maine brewers are well practiced in this romantic fermentation method.

A coolship (koelschip) is a long, shallow vessel that hot wort (a mixture of malt and other brewing ingredients that will make beer) is poured into. The wort cools in the open-air vessel until it reaches the yeast’s preferred temperature and the right conditions for fermentation and the creation of beer.

Because the coolship is open, the beer is fermented by wild yeasts floating around in the air, which is why such beers are also called spontaneously fermented beers. This is unique because the yeast introduced to wort is usually carefully controlled and fermentation takes place in a closed tank. Spontaneously fermented beers are often aged for several years (lambic style) and might be a blend of several batches of beers aged from one to three years (gueuze style).

Rising Tide Brewing Co. recently released its second batch of Hestia, a spontaneously fermented beer with raspberries. I spoke with the Portland brewery’s quality control specialist, Missy Littlefield, to learn more about what makes this beer special.

Littlefield’s job is to ensure that beer quality at Rising Tide is consistent. She does this by analyzing beers from a microbiological standpoint. She checks fermentation by taking a gravity reading. Beers fermenting in a tank are checked once a day and beers aging in barrels are checked once a month until they reach the desired gravity, when they are then allowed to age.

She explained that the wort for Hestia was poured into two maple syrup cooling trays (retrofitted with a screen to keep the wort safe) that were located behind the brewery and where it was cooled and fermented by wild yeasts. Once fermentation was complete, it was then aged in barrels. Hestia was created from a blend of beer from four different barrels filled between 2016 and 2018.


Littlefield started working in the lab six years ago, and the first time she viewed a spontaneously fermented beer up close, she said, it was a bit scary. Normally she strives to ensure that no wild yeasts or bacteria show up in her samples, but with Hestia and other coolship beers, she checks to make sure that these organisms are present and doing well.

I tasted Hestia on tap in the Portland brewery and from a bottle, along with spontaneously fermented beers from fellow Portland breweries Allagash and Liquid Riot. You can also find examples of coolship beers from Newcastle-based Oxbow Brewing and Sidereal Farm Brewery in Vassalboro.

Coolship beers are among my favorites because they are like drinking a time capsule. The yeasts that ferment them were in the air at a specific time and place. Here’s what I thought of the three I sampled:


Style: Fruit beer

Tasting notes: Beautiful pink with a white head. Smells like over-ripened raspberries with a hint of vanilla and slight funk. Tastes like raspberries and is slightly tart and funky.



Style: Spontaneously fermented ale

Tasting notes: Light gold with a white head. Smells funky and fruity, like apples, earthy and vinous. Tastes like apricot, fruity and funky with a hint of lemon. Dry and tart.


Style: American spontaneous beer

Tasting notes: Light gold, thick white head. Smells fruity, funky, vinous, barnyardy with a hint of honey. Tastes fruity, funky, vinous and barnyardy. Dry, with high carbonation, tart and tannic.

Caitlin Enz is a Certified Cicerone® who lives in Portland. Follow her on Instagram at @hops_and_brains.

Only subscribers are eligible to post comments. Please subscribe or login first for digital access. Here’s why.

Use the form below to reset your password. When you've submitted your account email, we will send an email with a reset code.

filed under: