It’s common for geologists to discuss the most recent geological happenings over a cold one around a campfire after a long day of doing field work. So when my friend Nick, a historian and homebrewer, mentioned the long lost technique of using hot rocks to make beer, my response was naturally “so when are we doing it?”
Stein brewing is a method brewers used before they could direct-fire brew pots, mostly because they were made of wood. In lieu of heating the pot, brewers used hot stones to heat the wort. One serious problem brewers faced was the dangerous potential for the stones to explode or fall apart during the heating/cooling process if the correct type of rocks are not used.
So this summer, Nick and another friend, Brian, came over to brew a stein beer. Nick developed the recipe, an American stout. We wanted something that could benefit from the caramelization of the sugars when the super-heated stones came in contact with the wort and also add a slightly smoky character that can sometimes develop from the ash.
We started the campfire about two hours before we mashed in and added anthracite coal to add extra heat without producing too much smoke. On a grate in the fire, we heated eight igneous rocks (fine-grained Triassic diorite), which we rotated in shifts of four. The Triassic diorite is the bedrock of my farm and is perfect for stein brewing because it was born of magma, so when cooling from high temperatures its interlocking crystals are just begging to get heated again. The Triassic birth of these heat-loving rocks also adds to the drama — dinosaurs just began to roam the land, Pangea just began to break up, the crust began to crack, earthquakes . . . sorry, I got carried away, back to the beer making.
We used the brew-in-a-bag method for our mash and heated the strike water with a propane burner. After the hour mash, we added the first round of stones. We rotated the stones every five minutes to maintain a boil and this is where the strainer that came with the pot was very useful by allowing us to easily lift the hot stones out of the wort. After a few rounds of boiling, the rocks turned dark from all the caramelized sugars on them (and they smelled pretty good in the fire too!).
At the end of the boil, we chilled and took a gravity reading. One variable we didn’t account for was a lower boil-off rate from not having the same constant boil the burner provides. So, instead of 5.5 gallons (21 L) of 1.051 wort, we ended up with 6 gallons (23 L) of 1.047 wort, which we felt was not bad for changing a pretty big part of the brewing process.
After primary fermentation we split the beer into three batches to do some one-off experiments. We added 3 oz. (85 g) of cold brewed NoCO2 Peruvian Dean’s Beans Coffee to 1 gallon (4 L) of wort, dry hopped another gallon (4 L) with 0.25 ounces (7 g) of Centennial hops, and kegged the rest as was.
The finished beer turned out really well. The original stout was roasty and caramel, and the citrus notes of the Centenial hops played really well with the roast in the stout, making the dry hopped version more like a black IPA. The coffee really stood out in its portion; there were nice vanilla, roast, and peppery notes from the cold brew, and was the favorite among a group of us.
Sure, stein brewing is labor intensive, but it allows the brewer to interact with the beer in a whole different way and adds a very unique character to the beer. Plus, it makes a great story, which is half the fun of homebrewing.