All About Beer Magazine - Volume 22, Issue 1
March 1, 2001 By

Last fall I was invited to visit and judge homebrew with the Music City Brewers of Nashville. They shared beer, stories and food with me; and I was a guest at Bosco’s Brew Pub in that fair city. In that interim, I became better acquainted with Bosco’s most famous beer, Flaming Stone Beer, America’s Original “Steinbier”; and owner Chuck Skypeck, who developed the beer.

Modern brewers fabricate, or ferment, their beer from malted grains which have been crushed or milled. Malting is the process of activating important enzymes in those grains which are necessary to preparing them for brewing use. These malts are then steeped in water of various and increasing temperatures in a process called mashing. Mashing actually changes the grain’s properties to produce a fermentable liquor called beer wort. This beer wort is then brought to a full boil to stabilize the grains’ proteins, and incorporate the hop resins into beer to protect it from harm later during the fermenting process.

Boiling the wort is a fairly recent brewing technique dating only from about the 15th and 16th centuries, probably when brewers found that beer fermented from boiled worts had better keeping qualities than other beer.

By contrast, stone beer or steinbier is beer made by a centuries-old method dating from the early days of brewing before metal kettles of suitable size were available, and even before beer worts were actually boiled. The mashing program involved heating the mash slowly through the temperatures above 90 degrees F/32 degrees C, and especially in the range 113-140 degrees F/45-60 degrees C, and on upwards to activate, first, protein, and later, starch conversion enzymes (140-167F degrees/45-75 degrees C). Heating the mash above those temperatures serves to inactivate these enzymes. Of course those old brewers had no knowledge of enzyme activity and temperature ranges, but they knew what worked.

The stone brewing system involves adding superheated stones to beer wort to effect mash conversion temperatures. Bosco’s Flaming Stone Beer is a rare example of a brewing style which has all but vanished from the planet.

The Stone Brewing Saga Still Lives

In Finland, the stone brewing method is still used to produce sahti, a strong beer of 7 to 10 percent alcohol by volume (abv). Sahti, once a popular and commonly homebrewed beer, is made in relatively small batches (10 to 40 gallons). Old “sahti masters,” most of them women, work in home sauna breweries to brew for a single festive occasion (sahti doesn’t keep well).

The sahti mash starts by placing ready crushed, commercially produced malt in the long aspen wood kuurna, or lauter tun. The kuurna is layered with straw and juniper branches that are sometimes sprinkled with hops. Heated water is added, and upward step infusion mash temperatures are achieved by the addition of hot stones from the sauna over a 4-hour period, until conversion is reached. Traditionally, the beer wort is never brought to a boil except for the occasional quick boil at the end of the process. The beer is fermented with Finnish baker’s yeast in 10-gallon aluminum milk cans. Other similar, but rarely brewed, indigenous beers include Norwegian juniper ales, Swedish gotlandsricka and Russian kvass.

The use of heated stones to brew beer in Austria is documented as recently as 1910. That system involved adding hot stones to heat and control the mash wort temperature. Often, this included “roasting” hops added atop a layer of stones, seated on juniper branches, placed in the mash before adding the liquor. Parts of the mash were actually parboiled as the rocks were added (perhaps a precursor to decoction mashing). The grist in this system was equal parts of barley, wheat and oat malts. The stone brewing mashing method was probably used until late in the 19th century in such northern European brews as Berliner weiss, broyhan, and graetzer styles featuring non-boiled worts.

Rauchenfels Steinbier

Modern stone brewing was first revived in Germany in 1982 by Gerd Borges of Rauchenfels Brewery in Neustad, Bavaria. He had found the 1910 Austrian brewing text mentioned above and then had the astoundingly good fortune to find the son of the last brew master of one of those breweries. The old man, who died in 1965, had made an audiotape of the process.

Borges was able to purchase the audiotape AND the nearby rock quarry where the special graywacke stones (a type of sandstone) are found. These high strength, low porosity rocks can be heated to 2,200 degrees F (1,200 C) and then cooled to 212 degrees F (100 C) without exploding. Using this information, Borges incorporated the method into the brewing system of his newly acquired Werner-braü brewery in Neustad, where he built equipment to heat and handle the superheated rocks during the wort boil. The mash for this beer was done in the usual fashion with exact temperature control.

The rocks are heated by beech wood over a 12-hour period. They are not employed until the wort has been brought to a near boil.  Then they are deposited in the brew kettle to finish that boiling process, during which the stones adsorb caramelized sugars. Following this, the stones are removed, cooled and stored until they are reintroduced to the beer at the end of the lagering period. This allows the sugars to be fermented and added to the beer’s body, giving it the characteristic smoky toffee-like flavor for which the beer is famous. The beer, Rauchenfels Steinbier, was a commercial success and has been well received both in Germany and abroad.

Skypeck’s Early Stone Beer Experiments

Chuck Skypeck developed an interest in this brewing style early in the last decade, when, as homebrewers, he and a friend, Phil Rehn, started experimenting with stone brewing methods. He was a former sales representative with DME brewing systems manufacturers, waiting to get Tennessee’s first brewpub license for Bosco’s Pizza Kitchen. Their first homebrew experiments failed because the stones in the Tennessee valley, mostly porous limestone, were unsuitable for the purpose. However, the region’s quartzite rocks were useable when heated in the coals of an oak wood fire. Their successful homebrew efforts are documented in Zymurgy magazine’s winter 1992 issue.

The beer recipe they chose for these experiments was Rehn’s award-winning altbier with reduced hop levels. They contacted Borges, who declined to send them the graywacke stones but recommended that they try granite. They used 2-pound stones the size of oranges, so as to fit them into their soda canister fermenters. Skypeck and Rehn were encouraged in their experiments by the brew master at Rauchenfels, who sent them the old Austrian brewing text mentioned earlier.

Bosco’s opened in 1992, but it wasn’t until mid-1993 that Skypeck found time to experiment with stone beer. He settled on Colorado pink granite rocks, half the size of bowling balls, for the first commercial attempt at stone brewing in September of 1993. It was to be an Oktoberfest brew. The stones were heated for three hours to 700 degrees F (480 C) in the company’s oak-fired pizza oven. After the mash, and just before the boil, the red hot rocks were added to the wort as it drained into the brew kettle. As one might imagine, there was a huge cloud of steam, with much hissing and popping.

The wort was boiled for an hour and a quarter. At the end of the wort boil, the stones were removed and stored in the freezer. They were added back at the end of the ferment, giving a unique touch from the etched sugars, which contributed caramel flavor and body but no smoky character.

Skypeck has never managed smoky character in his stone beers, and he now believes that Rauchenfels uses smoke malt to achieve that effect in its definitely smoky steinbier. He told me he doesn’t think the stone brewing process actually adds smoky character to beer.

Good Public Relations

The new beer was well received, with two local television stations and National Public Radio in attendance. There was even a story in USA Today.

Even though this was intended to be a seasonal Oktoberfest brew, Skypeck soon realized that the stone-brewed beer had provided a splendid public relations break for his new brewery. He decided to make it a regular house specialty. His judgment was confirmed when the 2,170-gallon first batch lasted a mere six days. It was to become their “training wheels” beer, an easy-to-drink introductory beer, for initiates to the microbrew scene. Indeed, it outsells the brewpub’s other beers by a 3:1 margin in Memphis and 2:1 in Nashville.

The stone beer at Bosco’s in Nashville is finished out in a slightly different manner. The sugar-coated rocks are not added back to the fermenting beer. Instead, they are used in the next brew to add their character in the mash tun at the beginning of the brew. Bosco’s Flaming Stone Beer starts with a wort density of 12 percent fermentables (mostly Pilsner and Munich malts). Hallertauer hops provide the 16 IBU (international bittering units, or ppm alpha acids), leading to an alcohol content of 4.8 percent abv.

The pub offers an excellent menu featuring fine pizza and other good basic fare at a reasonable price. Skypeck is working hard to improve all of his Bosco’s brews at the two locations (Memphis and Nashville) and, to this end, he has hired renowned German brew master, Fred Scheer. Fred’s influence is becoming apparent with the beers at Nashville.

Scheer, a relative newcomer to the British brewing styles that dominate Bosco’s beer menu, is fast becoming skilled in producing cask-conditioned ales, which are promoted during the happy hour Monday through Friday. He also does an excellent and very credible IPA.

Author’s note:  Bosco’s Pizza Kitchen & Brewery is located at 7615 W. Farmington, Memphis, TN 38138; phone 901-756-7310. Bosco’s Nashville Brewing Co. is located at 1805 21st Ave. South, Nashville, TN 37212; phone 615-385-0050; www.boscosbeer.com.


Fred Eckhardt
Fred Eckhardt lives, writes about and drinks beer in Portland, OR. He is the author of The Essentials of Beer Style and Saké.