From the Pores of Earth — The Impractical Alchemy of Stone Fermentation — Good Beer Hunting

When Aaron Reames stopped by the Sonoma Cast Stone booth at the 2015 Craft Brewers Conference, he was immediately enticed by the promise of stone fermentation.

“It was a really new medium to work with,” Reames says. “You think about that rock flavor, that stone subtlety, the zinc subtlety that could actually augment something that has a tartness and actually give it a more robust, rounded flavor.”

Reames knew enough about the science of stone fermentation to get excited. Before opening Bent Water Brewing Company in Lynn, Massachusetts, Reames studied molecular genetics and biotechnology. He wanted to open a brewery that focused on water character and mineral composition—things that could differentiate Bent Water from the legion of other breweries opening across his state. When he saw the egg-shaped Sonoma fermenters, he geeked out, gabbing with the rep about the acid-alkaline response that happens between wine and stone and how bacteria in the pores of the material could make for a new dimension of sour beers. Reames bought two 15-barrel, charcoal-black vessels and set them up as the centerpiece of Bent Water’s beer portfolio.

At the time, stone fermentation was a percolating trend. Stainless steel and wood had ruled the scene long enough, and breweries had begun to experiment with concrete, slate, granite, and clay. Great Lakes Brewing Company, Dogfish Head Craft Brewery, and Benson Brewery had all started brewing with amphorae, leading All About Beer to wonder if clay fermentation was the next popular frontier in craft beer. Meanwhile, Allagash Brewing, Tired Hands Brewing, and Russian River Brewing invested in stone fermentation tanks, taking cues from European vintners. BeerAdvocate wondered if this marked the threshold of “new flavors to explore.”

In addition to acquiring the new equipment, breweries developed novel techniques and collaborated with academics to get the processes right. They studied the nexus of rock, water, and beer, bringing the three into sharp focus. But despite carefully researched efforts, stone-fermented beer never rose above an offbeat curiosity in the beer world. The predictions never came true.

As brewers soon discovered, stone is a clumsy fermentation medium. It’s heavy, expensive to manufacture, and easily corroded. The allure of the minerality it imparted was never realized. And it probably never will be.

Brewers are well-acquainted with the benefits of stainless steel and wood. Steel is predictable, inert, and perfect for industrial brewing. Wood has character. It breathes as the beer rests inside. But neither has the kinship of rock and beer. Something primordial comes alive when wort and yeast meet stone.

That’s probably why geologists often get up close and personal with their specimens, as Andrew Thomas, a zinc analyst, points out.

“Any geologist that ever picked up a rock has licked it,” he says. Rocks have pores, which offer insight into the environmental conditions, groundwater, and even animal life of an area and a time period. “You have to ask yourself, am I tasting mineral-like salts of some sort in the pore system, or am I tasting something else in the pores of the rock?”

Rockhounds can pick up details of a mineral with a single swipe from their taste buds. Halite is salty. Pyrite tastes like hard-boiled eggs. Getting a metallic flavor? That may be melanterite.

Brewers are accustomed to stripping the earth out of their beer, filtering it and using reverse osmosis to erase the legacy of hard surfaces it has permeated. Even with ever-more-complex flavors and compounds broadening the modern beer palate, these rock-borne flavors are novel territory. That’s why Reames lit up when he saw that Sonoma, after decades making wine vessels and architectural concrete, had launched a line of brewery-sized fermenters, which the company claimed could offer “a renaissance of innovation, producing an exciting, new generation of wild beers, sour beers, meads, and porters.”

What seemed to Reames like the cutting edge of fermentation technique was actually common knowledge among European winemakers, explains Dave Jensen, Sonoma’s director of research and development. Sonoma started making concrete fermentation vessels, he says, because American wineries didn’t want to pay international shipping on heavy units from Europe. Soon, they became a must-have in the market. Beer makers followed suit, and brewers started approaching Sonoma looking for a distinguishing element in their brewhouse. Sonoma acquiesced and in 2015 attended the Craft Brewers Conference for the first time, in an attempt to win over a new generation of curious brewers.

“A lot of European winemakers never quit using stone and concrete for fermenting and storing,” Jensen says. “They added wood to it, but they never really left that old way of doing it. Only over here does it seem like a new invention.”

The Samuel Smith Old Brewery in Tadcaster, England, is a bastion of stateliness and decorum. It employs a full-time cooper to make its barrels, and mashes in copper tuns. Local deliveries arrive by shire horses. And all of this happens 85 feet above an underground limestone lake that has blessed the British brewery with a current of perfectly conditioned water to make its standard-bearing Porters, Pale Ales, and Oatmeal Stouts for the past 265 years.

Samuel Smith doubled down on the limestone-filtered water by adopting rectangular, open-top fermenters, known as Yorkshire squares, made from Welsh slate, which keep yeast in suspension during primary fermentation. The combination of limestone water and slate vessels became a signature of Yorkshire brewing. When Black Sheep Brewery opened in nearby Masham in 1992, it continued the Yorkshire tradition and invested in six 50-BBL slate squares. According to Black Sheep head brewer Dan Scott Paul, the combination of the limestone water and the slate fermentation gives Black Sheep’s and Samuel Smith’s stone beer its trademark dry, flint-like finish.

“The water content is quite high in carbonate and bicarbonate, but also high in sulfates. And sulfates add a dryness to the palate as you drink the beer itself,” Scott Paul says. “That, coupled with the Yorkshire square dryness, adds another complexity to the mouthfeel.”

Black Sheep was immediately popular and grew at a rate that its Yorkshire squares couldn’t support. The Hardys & Hansons Brewery offered additional squares for free, provided Black Sheep could transport them without any damage. Other breweries in the area had long given up on slate squares, despite the sensory benefits, preferring to adopt Yorkshire’s other great gift to brewing: stainless steel.

Stainless steel was discovered by Sheffield native Harry Brearley in 1913, and the first beer was fermented in a stainless vessel in 1928. The alloy had many advantages over stone or wood. It was resistant to corrosion and easy to clean. It was also easy to manufacture and much lighter to ship. By the 1970s, breweries in England had updated to the newer, more reliable material of stainless steel. The tradeoff was that stainless lent no character to the final product.

Brewers were eager to make that trade, and stainless is now a ubiquitous presence in breweries worldwide, to the point where slate vessels have largely disappeared. Instead of struggling along with Yorkshire squares, Black Sheep came up with a new kind of vessel called Yorkshire rounds. Although these rounds encourage the same yeast activity as Yorkshire squares, there are two notable differences: Rounds are circular and—crucially—made from stainless steel. Scott Paul says this material helps produce a more modern style of beer.

“The only discernible difference was, because of the slate squares themselves, we had to sort of monitor temperatures a bit more radically,” Scott Paul says. “It was a bit harder to control the fermentation temperatures in the square vessels, so arguably the consistency of product is better.”

Black Sheep was far from the first British brewery to eschew slate squares in order to grow. Along with Hardys & Hansons, every other major brewery has moved on to conical stainless steel. Even Tetley's Brewery, another Yorkshire stalwart that had been using Yorkshire squares since the 1880s, destroyed its slate vessels in 2008.

In early May, Black Sheep went into receivership, citing a rising cost of production among the reasons for its insolvency. The Yorkshire brewing tradition, though distinct, was not enough to sustain the brewery through the pandemic. The owners hope to sell the brand to another steward, but there’s no telling what this means for their already diminishing tie to the stone formations that have defined the area’s beer for centuries.

Today, if you want to taste the way Yorkshire limestone and Welsh slate come together to make a mineral-rich, almost fruity beer, you may have to track down a shire horse.

Brian Zimerle is not a beer snob. He homebrewed once, but he mostly sticks to readily available go-to beers. As a ceramic artist who specializes in recreating historical pottery, he’s most captivated by watching pieces come together.

Chemical analyses on shards of pottery discovered in China show that, as long ago as 7000 BCE, people were fermenting alcohol in clay. Archaeologists have studied these shards as a window into the roots of humanity’s relationship with alcohol. When Great Lakes Brewing Company’s Pat Conway and University of Chicago archaeologist Tate Paulette approached Zimerle in 2012 to help reconstruct a Sumerian brewing vessel, he signed on not for the beer, but for the history.

The beer they aspired to recreate was based on the Hymn to Ninkasi, a song that pays tribute to the Sumerian goddess of beer. Dating back to 1800 BCE, the hymn is considered to contain the oldest surviving beer recipe in the world. Great Lakes was not the first brewery to attempt to brew from the Hymn to Ninkasi: Anchor made a Mesopotamian-style beer in 1988, and Dogfish Head had also been reviving recipes from the dawn of civilization through its Ancient Ales program, working with molecular archaeologist Dr. Patrick McGovern.

Zimerle gave his nights and weekends to studiously laying down coils of clay. Called a gakkul, the ovular fermentation vessel he created was modeled after artifacts unearthed in Iraq in the 1930s. Each finished vessel was about 3 feet tall and required 30 to 40 pounds of wet clay to make. For Zimerle, the exercise was more of an artistic pursuit than a geological one.

“It's kind of like a hobby, a fascination,” he says. “You look at a material, and you wonder how that material came to be, through whatever process that these people had at that time.”

The first batch of beer was sour and over 15% alcohol, containing what Zimerle called “a crapload of bacteria.” Never commercially available, it also had a grainy, milky sediment. This was partly due to the outdoor fermentation, and partly due to the clay.

“There was staining on the walls of the vessel,” Zimerle says. “It was kind of like if you look at a coffee mug that you drink coffee out of regularly, and you kind of see that faint kind of dark brown at the bottom edges.”

Conway refined the recipe. In 2013, the brewery released Enkibru, whose Untappd listing touts its “vinegarish aroma.” In 2019, Great Lakes tried again, releasing a version it called Gilgamash, but even that was a limited release. Without the production capacity of a brewery like Dogfish Head, Great Lakes has kept its clay fermentation as a side project—a black sheep in its brewing program.

The converted barn at 7 Fox Hollow Road in Oxford, Connecticut, is a menagerie of fermenters.

Two 500-liter (4.2-BBL) terracotta amphorae stand alongside foeders and Sangiovese casks. Coolships bubble over just across from two gigantic, dimpled-granite fermenters—one a blue-grey, striped Bavarian granite and another made of dappled, rose-colored Spanish stone. Elsewhere, a rectangular open-air concrete cistern sits ready for its next batch of Saison. This is OEC Brewing, the playground of owner and head brewer Ben Neidhart, a distributor-turned-Willy-Wonka whose love of spontaneous fermentation led to him acquiring the most eclectic collection of fermentation vessels on the planet.

“One of the things that really always attracted me to sour beer is how much of a natural process it really is,” Neidhart says. “I like those techniques. And I'm willing to experiment with it.”

“OEC” stands for “Ordinem Ecentrici Coctores,” a bit of faux Latin that translates to “the Order of Eccentric Boilers.” Some of the eccentric boils include Malefactus Amphore Domitare Still Ale, a tannic, wine-like dark Sour oxidized in Etruscan clay pots, and Spontalis Roseus, a Lambic-style blend made from beers spontaneously fermented in a coolship, then in oak barrels, and finished in the pink-granite fermenter. Neidhart says the last leg gives the beer a fruity or peppercorn flavor that’s unlike anything that could be accomplished in wood or stainless steel.

When OEC opened in 2014, Neidhart was among the group of brewers who saw stone fermentation as the next horizon in beer making. Around the same time, in Minnesota, Schram Vineyards Winery & Brewery started using its square concrete fermenter to brew IPAs. In 2019, One Fermentary opened in Minneapolis, piggybacking on the excitement created by Schram with its own Sonoma Cast Stone egg. The brewpub invited local breweries to truck in their wort and try the stone for themselves, and in months it was making a stony Helles with Surly Brewing Co., an IPA with Gewürztraminer grapes with Dangerous Man Brewing Co., and a light Wheat Ale, half-fermented in concrete, made with the Brewing Change Collaborative. Bent Water’s two eggs yielded fascinating beers like Concrete Evidence, an 8.9% ABV Brown Ale that was formulated to mimic the minerality imparted by British limestone, and a triple-dry-hopped take on its flagship Thunder Funk West Coast IPA, whose “river rock” character, Reames says, played well with the citrus notes.

The half-decade dalliance between stone and craft beer resulted in some fascinating beverages, but ultimately not enough to sustain the cost of curiosity.

One Fermentary closed a year after opening, and the egg went up for auction. When StormKing Brewpub and Barbecue opened in the same space in 2021, the egg was gone, sold to Black Frost Distilling in New Ulm. Schram has since opened a taproom dedicated to beer, though brewer Brian VanHout has yet to try a beer in the concrete vessel. Sonoma has moved on to new concrete formulations and geometries to try to recapture some of the excitement of 2016, but Jensen says that some customers may have discovered that the tanks created “too much distinction” from mainstream beers. Even OEC is rarely using its concrete or granite fermenters, with Neidhart saying that, because of the porosity of the stone, the tank is almost impossible to clean, and the extra effort does not result in better sales.

Bent Water put its two charcoal-black eggs in storage, citing the need for more efficiency as it has grown. Brewing in eggs is expensive, Reames says. Not only does fermentation take longer, the cleaning is more delicate, and the eggs take up a lot more space than traditional stainless vessels. While Reames was once excited about the new palette of flavors, he didn’t see that translating into sales, as ultimately, drinkers don’t value the stone flavor enough to compensate for the added cost.

“It's easier to condition in two to three stainless steel tanks than it is to condition in the concrete tank,” Reames says. “It’s definitely unique, and there are some really great tasting beers that you can make with it, but it has to be a labor of love.”