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What the heck is a turbid mash?

A funky old Belgian brewing technique explained.
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Photo courtesy of Jester King Brewery

Photo courtesy of Jester King Brewery

While brewers in the U.S. have gleefully adopted the names of site-specific beer styles like Baltic porter, Scottish ale and Berliner weisse, many have been hesitant to do the same for the wild ales of Belgium: lambic and gueuze. Part of that is likely due to the difficulty of replicating those beers stateside. If you’ve been lucky enough to try a beer from classic lambic producers such as Cantillon or Boon, you know it: There’s just something different about them.

While that difference has much to do with the wild microflora native to Belgium that are used by the country’s lambic producers to ferment their beers, a technique known as turbid mashing also plays a significant role.

The history of the turbid mash goes back to 1822, when the Belgian government, in its infinite wisdom, decided to tax the country’s brewers based on the size of their mash tuns. This had a couple results: Brewers immediately bought or built the tiniest tuns their brewing capacity would allow, and they devised a technique to stuff the vessels as full of grain as possible. This method became known as the turbid mash, named for the milky, murky appearance of the wort it produces.

The process of turbid mashing begins with a grain bill heavy on raw, unmalted wheat. This is then stuffed inside the mash tun with a relatively small amount of water. The cementlike mixture is mixed—carefully—and then a portion is removed and heated. This is the historic part: Because the standard false bottom on most mash tuns that allowed them to draw off wort from the bottom of the vessel wasted too much space, brewers instead removed the brewing liquid from the top of the mash using a stuikmand—a tall wicker basket that was pressed down into the mash to act as a colander, allowing it to fill with liquid while keeping the grain out. (In this way a turbid mash differs from a decoction mash, another traditional mash procedure that requires the malt be boiled as well.) The wort inside the stuikmand was moved and heated in a boil kettle, many of which were outfitted with chains that dragged along the bottom to keep the thick sediment from sticking and scorching. The hot liquid was then added back to the main mash, and the process was repeated several times.

While the Belgian mash tun tax was repealed in 1885, many traditional lambic brewers still employ turbid mashing to make their wild ales, and several American breweries—including Jester King Brewery, Deciduous Brewing and Funk Factory Guezeria—employ the technique. This isn’t an easy task. “A lot of America brewhouses aren’t really set up to do a turbid mash,” says Funk Factory Gueuzeria’s Levi Funk, who produces his lambic-style ales using the technique. “That first dough-in is really, really thick. It’s sheared pieces off the mash tun equipment at some breweries where we’ve tried it.”

Also: “It’s a bitch of a brewday,” Funk says. “It’s a long, long brewday. We’re talking 15, 16 hours.”

So why go through the trouble? Because it’s the only way to make a lambic with lasting quality, Funk says.

The result of all that mixing and boiling and remixing and reboiling is a wort packed with long-chain carbohydrates, sugars unfermentable by normal brewing yeast. This is a good thing because it provides food for non-normal brewing yeast and bacteria—funk-forming Brettanomyces and acid-producing lactobacillus and pediococcus, for instance—to slowly digest over several years. And that’s extremely important for beers meant to be aged for long periods of time.

“In my opinion, turbid mashing doesn’t even show benefits until two years in the bottle,” says Dave Sakolsky, owner and head brewer at Deciduous in Newmarket, New Hampshire. He admits it’s a lot of extra work to undertake for something that may not show any difference until two or three years in. “But one, it’s a labor of love, and two, I’d hate for somebody to come across one of my beers that’s six years old and it tastes terrible, when I could’ve avoided that by just doing a turbid mash.”

Funk agrees: “There’s a lot of discussion about whether a turbid mash is even necessary. Couldn’t you just do a decoction with the intent of creating traditional unfermentables and get the same result? People have tried that, and the answer speaks to the product: It just doesn’t hold up very long. Is it a bad product? Not at all. It’s just different.”

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