Here’s something you won’t read often in a brewing magazine: You won’t need any fancy equipment for this. The ancients who heated their mashes with stones were not making beer on the latest Ss Brewtech kit. In fact, since you’ll be playing with red-hot stones, it’s probably best to leave your nicest gear out of this.
There are, however, some decisions to make and a few important things to keep in mind, related to ingredients, equipment, and personal safety. (For much more on mashing with hot rocks, see Fire & Brew Stone: The Real Story of Steinbier.)
Which Malt to Use?
You could simply buy some good pale malt. After all, the type of malt isn’t necessarily the point here — this is about getting together with friends to perform a traditional, dangerous, and highly photogenic technique.
The suggestion from Simonas Gutautas, a brewer with Dundulis in Lithuania, is to go with a relatively less-modified pilsner malt. That’s what they use at Dundulis when they brew about 20 hectoliters (17 barrels) of traditional stone beer four times per year.
Gutautas says they use undermodified pilsner malt sourced from a local farmer, and they find that it makes the lauter easier. Think of it like a decoction: Today’s highly modified malts are meant for infusion, not for getting boiled — which is exactly what happens, in brief pockets, when you add hot stones. “If you use Maris Otter, you will have a mass, like clay,” Gutautas says.
You can also opt for something old-fashioned from any number of small-batch maltsters. Sugar Creek Malt in Indiana, for example, sells some interesting products made from unusual grains or inspired by older traditions. These include einkorn malt, oven-dried rye malt in the Baltic or Russian style, and smoked-oat malt inspired by what the stone brewers of Carinthia once used.
If you want to get even more serious about authenticity, you could source local grain and malt it yourself (see “Malt Your Own Barley,” beerandbrewing.com). That’s what some of the traditional farmhouse brewers in Northern Europe do, though their methods vary. Often, they involve wood fires that inevitably add smoke character. Even if you’re buying malt, some portion of smoked may be worth including. Lars Marius Garshol’s book, Historical Brewing Techniques, includes three recipes for stone beer; two feature smoked malt meant to approximate farmhouse-malting methods.
Here’s a tip from Gutautas: If you want to stick with pilsner malt yet add some color or smoky character, you can do that using the hot stones. He says the red-hot ones will help darken the beer while adding some burnt character and smoke. To add more, you can carefully put some dry malt or rye flour on the stones first — literally roasting it a bit before it goes into the mash.
Notable: You want a nice, stiff mash — the kind in which your mash fork can nearly stand up on its own. If it’s too thin, the hot stones will quickly sink and burn the bottom.
What About Hops?
You have a lot of leeway with hops, depending on what you want to try or which tradition you want to emulate. Many traditional brewers in Scandinavia and the Baltics brew a separate hop tea, then add it to the wort afterward. Gutautas says that you can also save some of the tea for the next day, to blend versions that are more of less hoppy or bitter, according to your taste.
He also suggests using whole-leaf hops; you can then use the spent hops in the filter bed to help the lauter. If you want, you can add the hop tea directly to the mash. You can also skip the tea and simply add hops to the mash, where the hot stones will handle some of the isomerization.
Or, if you’re going for ancient, you could skip the hops altogether and try a gruit-like mixture of flowers and herbs.
What Kinds of Stones?
We are not geologists, but we know there are two things to avoid here: The kinds of rocks that explode when heated in fires and the kinds that fracture into many tiny pieces — because some of them will inevitably crack in the mash tun. Apparently, this is just part of the deal.
Without getting into specific types of rock — because there are no guarantees — what you want are harder, more dense stones, not the more porous, permeable ones. (No lava rocks.) Just to be on the safe side, please use eye protection.
Gutautas suggests using stones that are roughly the size of fists, if possible — you want them to have a decent surface area, but you also want to be able to manage them with tools as safely as possible.
How to Handle the Stones?
“You need tongs of some sort to handle the stones, preferably with some length,” says Garshol — who wrote “Fire and Brew-Stone” (page 20) and who has visited farmhouse brewers who still mash with hot stones. “Some use baskets. You can use wooden tongs, but those then need to be well soaked in water first and are likely to catch fire anyway. ”
The kind of large steel tongs that you might find next to a fireplace may be best. A shovel might also be useful. At Dundulis, Gutautas says, they use a pitchfork.
Also, wear PPE. “You want to be absolutely sure that under no circumstances will you risk touching the stones,” Garshol says. “Protective boots and gloves are good. Naked skin is not. ”
One more tip: It’s understandable to make this a festive occasion of sorts and have a few people watching, but the brewer ought to be sober and the designated rock-handler. “Drinking while brewing stone beer is a really bad idea,” Garshol says.
What’s the Ideal Mash Tun?
For the mash tun, don’t use your finest stainless and definitely don’t use your converted Igloo cooler. You need something that won’t melt and can handle some wear and tear. We suspect a sturdy keggle-type tun that has seen some mileage would work just fine.
However, the ideal vessel — for tradition, for function, and for style — is a large wooden tub of some kind. Even at Dundulis, they brew in two large wooden vats.
If your local brewery is unloading spent barrels for a song, one of those (possibly sawed in half) might do the trick.
Your choice of a mash tun is relevant to the next question…
How to Lauter?
It sounds pretty cool to throw some hot rocks into the mash, but… what then? How do you separate that precious, sugary liquid from that pile of warm rocks and sizzled grain? The ancients might have scooped out the liquid with jugs, but clearly there are more efficient ways to go about this. We’re brewers, after all. This kind of problem-solving is where we are, as they say, Vikings.
One advantage of a well-worn keggle tun is this: It probably has a false bottom and a spigot already. Likewise, drilling one into a wooden tub isn’t too difficult. A screen over the inner opening might help, or some juniper branches, sticks, or straw could provide a natural filter bed while adding a bit of their own character.
Boil the wort if you want — or not. If you’re going raw, here’s an interesting tidbit from Gutautas: An unboiled stone beer tends to wind up clearer than other raw ales, which are often cloudy with suspended proteins; it’s plausible that boiling-hot rocks facilitate a kind of hot break in the mash.
For fermentation, a pitch of your favorite kveik would make sense, after allowing the wort to cool to about 100 ° F (38 ° C). At Dundulis, they use a culture that originated with the Lithuanian farmhouse brewer Julius Simonaitis (a version is available from Yeast Bay as WLP4046).
Opting for a mixed culture of yeast and bacteria could also lead to interesting results. Or — in a historically ungrounded callback to the Franconian steinbier that first caught the attention of Michael Jackson in the late 1980s — you could brew it as a clean lager, which could really allow those rock-sizzled Maillard flavors to shine.