Searching for Rock-Solid Foundations
The difficulty of finding stones that could take the heat was probably one of the reasons the style nearly died. Like the Steinbier brewers before him, Borges is able to use a type of sandstone found in Austria called greywacke, which was able to withstand the high temperatures -- up to 2,000 °F (1,093 °C) -- and the thermal shock of sudden cooling when dropped into the brew kettle.

Hot rocks used to boil Brimstone's Stone Beer are lowered into the wort in this keg. The "Swiss Keg," as it is known in the brewhouse, is permanently charred black from repeated heatings.

That rock was unavailable to Tewey. The only other brewery in the United States to brew stone beer, Bosco's (Germantown, Tennessee), used granite, but Tewey decided to start his own investigation by calling geologists at local universities. He asked them what types of rocks could withstand being heated to high temperatures and dropped into cooler liquids.

"What do you want to do that for?" asked one geologist at the Univer-sity of Maryland.

Tewey replied, "I'm going to drop the rocks into beer." The statement was met with stony silence.

Evidently, more than a few people contacted during his quest thought Tewey was a bit strange. He persisted, however, and was eventually pointed to a Virginia quarry that produced diabase rock, which Tewey was told would be suitable for his purposes.

Diabase is a volcanic stone often grouped with granite, though it has distinct components that set it apart. Its chief advantages in brewing is that it is strong and has low porosity. It also has a crystalline structure so that when it eventually breaks, it fractures cleanly into manageable slabs.

When Tewey called the quarry to price the rock, he was told that it was sold by the truckload -- quite a bit more than he needed for brewing. While Tewey negotiated for a smaller amount, the quarry manager asked, "What do you want it for?" Tewey replied, "I'm going to heat it up and drop it into beer!"

The quarry manager laughed and agreed to let him come down and take a few rocks.

Fire in Brimstone
Adding to the eccentricity of the style, the stones are held in a stainless steel, heat-blackened keg affectionately dubbed the "Swiss keg" because of the large holes drilled in its sides. The brewers place several large chunks of rock in the keg and then set it inside a 55-gallon metal drum for heating.

Wishing to be as true to style as possible, Tewey's method involved building a wood-fueled fire in the drum out in the parking lot at the beginning of the brew day and keeping it stoked for hours until the rocks were needed in the kettle. At least that's the way he did things until one day in September 1996, when a civic-minded neighbor smelled smoke and called the local fire department. The firemen arrived to find Tewey outside tending a fire in his 55-gallon drum.

"What's the meaning of this fire?" They asked.

"I'm heating rocks to drop into beer!" Tewey replied.

The firemen were evidently not too pleased with that answer; Tewey has since installed a gas burner to heat the rocks.

Modern Concessions
Unlike his historical predecessors, Tewey does not rely on the rocks to provide all of the heat for the wort boil; most of the heat is provided by the brew kettle's gas burner. Tewey used to add the stones to the wort toward the end of the boil by carefully attaching chains to the keg of hot rocks and hoisting it onto a forklift. The "Swiss keg" was then slowly lowered bottom first (the keg is topless). It caused quite a spectacle as it hit the surface of the wort, sending up a huge cloud of billowing steam from the kettle as the wort began a furious rolling boil. The rocks were allowed to stay in the kettle for a good 20 minutes, with steam pouring off the kettle the entire time.

Despite the drama of the large kettle, Tewey has lately revised his methods in the interest of safety. Now, portions of the wort are siphoned from the kettle into smaller tanks where the rocks are then added.

The rocks are still quite hot (hotter than boiling) when they are finally removed from the wort. They glisten with a new coating of caramelized sugars and dry quickly from their retained heat.

Cold Rocks Serve Second Duty
These rocks are stored in a freezer as the beer is force-chilled and pumped to the primary fermentor. After primary fermentation is complete, the rocks are slipped by hand through the hatch of the secondary fermentor, where they release their toffee-like caramel flavors into the beer over the course of a week. The average diabase stone survives two brewing cycles before breaking up into unmanageably small slabs.