Gearhead: Mills for the Grist

Cracking that barley kernel isn’t what it used to be. Today, brewers who want to dial in their grist and brew better, more efficient beer have a wide range of options. John M. Verive demystifies the increasingly complex options.

John M. Verive Jun 11, 2021 - 17 min read

Gearhead: Mills for the Grist Primary Image

Photo: Courtesy Ziemann

In the traditional English folk song “John Barleycorn,” the eponymous subject lives a long life and meets a grisly end—cut down at the knees, tied to a cart, beaten, hanged, drowned in a pit, tossed to and fro, and scorched by flame. But the worst indignity is yet to come for poor John. As told in the version by Steve Winwood’s Traffic in 1970: “But the miller he has served him worst and bad/For he ground him between two stones.”

As a personification of the cereal crop that shares his name, John Barleycorn’s story ends with revelry when he’s transformed into beer and whiskey. However, while half a dozen verses cover the harvest and processing of the barley, no mention is made of the brewing process, nor of the brewer. The song’s hero is the kernel with the seemingly supernatural power of rebirth—and why shouldn’t the barleycorn be eulogized by poets and rock stars? Just as humans have shaped the evolution of the grass, barley has shaped the evolution of human civilization; today, we’re still cultivating John Barleycorn and showing him our “deadly rage” of harvesting, processing, and malting him to brew our beer. Only the technology has changed: Now, the miller doesn’t use two stones but two (or four, or six) stainless-steel rollers.

Crushing It with Innovations

“It’s our dream brewery, and we spared no expense on what matters for the quality of the beer,” says Russian River founder Vinnie Cilurzo about their two-year-old production facility in Windsor, California, a few miles from Russian River’s famed brewpub in Santa Rosa. When discussing efficiency gains and a “big increase in quality” in flagship Pliny the Elder and house favorite STS Pils, Cilurzo points to the malt-handling system and a T-Rex wet mill from Ziemann-Holvrieka.

The wet mill is an ideal way to crush grain for brewing. Before the crush, some mash water is introduced to a steeping chamber to hydrate the kernels and activate the enzymes before the rollers do their work. It’s gentler on the husks, but wet mills are out of reach of most brewers (see “Malt Conditioning: Have Your Cake and Eat It, Too,”


The more common two-roll grain mill is as effective at the crush as it is simple: Feed the grist through two spinning rollers that crack the kernel, sheer the husk away, and crush the endosperm into uniform particles. It’s the first operational process in the brewery, and it’s easy to overlook its impact on beer quality.

As the complexity of the grain mill increases, so does the uniformity of the final crush and the granularity of the operator’s control of the precise particle size:

Add corrugations to the roller profile, and the husk will sheer off with less damage.
Add a second set of rollers to get a four-roll mill, and the first set cracks the grain and separates the husk while the next set pulverizes the kernel’s operative payload.
Add a sieve between the two rollers, and the smaller fragments from the first rollers are diverted before the second rollers re-crush the larger particles.
Add a steeping chamber to hydrate kernels before milling, and the husks slip off with minimal damage (contributing to smoother lautering and fewer astringent polyphenols).

The ideal result of the crush is to maximize the sugar extracted in the mash—small particles of endosperm mean more surface area and better enzymatic reaction in the tun—and to minimize lautering times, since more intact husks create a free-flowing grain bed. It is always a balancing act between extract efficiencies and time spent lautering. If brewers go too far with the grind to maximize extract, they risk a stuck mash and tannic off-flavors.



Russian River's Vinnie Cilurzo holds a handful of stones removed from malt by their pre-mill malt cleaning system.

Mind the Gap

“Brewers are always complaining about their efficiencies to me, but I just tell them to ‘mind the gap,’” says Ron Silberstein, founder of Admiral Maltings in Alameda, California. A brewer for 20 years before he turned craft maltster, Silberstein is as passionate about California barley as he is about beer. “Mind the Gap” is both the unofficial slogan of Admiral Maltings and a way to remind brewers of this: Although they’ve dialed in the crush for Rahr two-row on their mill, that doesn’t mean the small-batch product from Admiral will behave the same. Kernels of the California-grown strains are often smaller than those of commodity barley, with different “plumpness” and friability specs. (Higher friability means the endosperm is more brittle and will crush more readily.)

“To get the most out of the grist, you have to grind it properly,” Silberstein says.

At Pond Farm Brewery in San Rafael, California, founder and brewer Trevor Martens uses an RMS dual-roller mill to process the 800 to 1,000 pounds of grist for each 15-barrel batch. He appreciates how easy it is to “mind the gap” and get the perfect crush. Pond Farm uses Admiral malt in most of its lagers; the brewers have marked up the mill’s control panel with Sharpies to help them dial in the crush for their most frequently used varieties. They arrived at those settings through trial and error, and by visually inspecting the grist for every brew. Martens says that the crush room “smells incredible” whenever they’re working with the local malt and that it’s that intensity and freshness that make the more expensive malt worth the trouble.

Pre-Milled Malt

Admiral Maltings, like many other malt suppliers, can also take the chore of crushing off the brewer’s plate entirely with pre-milled grain. It’s an option that’s grown in popularity as new breweries have opened across the country, though Silberstein laments the compromise inherent in pre-milling. “It’s not the best for anyone,” he says, explaining that the brewers lose control over the grist, while the maltsters lose confidence that their product will be used before it stales or slacks.


Ian McCall, head brewer at Riip Brewing in Huntington Beach, California, agrees with that assessment, but he also sees it as a necessary concession to the business of brewing beer. Capital and space constraints in the growing brewery mean it lacks a dedicated mill and malt-handling solution. “Pre-milled grain is a nickel a pound more from BSG [Brewers Supply Group],” he says. Admiral’s pre-milled premium is the same. That’s $100 extra for a pallet of grain—but Riip is using only about a pallet of grain per week. “At some point, it makes sense to bite the bullet and spend 10 or 20 thousand dollars on a mill, but we’re not there yet.”

The pre-milled options at BSG have become so popular that the suppliers keep a stock of milled base malts to fill orders, while milling other specialty malts on demand. Ashton Lewis, BSG’s technical sales manager and a veteran brewer, says that the small increase in cost is often easier for brewery owners to swallow than the big expense of purchasing a mill. There are also labor savings and quality issues to consider.

The obvious downside to pre-milled grain, Lewis says, is freshness stability: “Whenever you pre-mill any cereal grain, you increase the ability of the grist to absorb moisture from the atmosphere, but it’s not really a practical concern.” BSG has conducted research and sensory tests on pre-milled grain, and Lewis says that even after six months, the pre-milled grain is within spec and passes sensory screening. The inventory of pre-milled grain is stored in barrier bags to minimize staling, and milled-to-order grains are stored in a humidity-controlled environment and shipped within a day of processing.

At Riip, McCall says he is cognizant of the freshness concerns—especially in a humid location a few hundred meters from the ocean—but the real downside for him is the extra work of managing inventory and ordering more frequently to minimize how much is stored.


Another upside to the pre-milled offerings at BSG, Admiral Maltings, and other suppliers is the consistency of the crush. Most suppliers offer a few different grades (fine, medium, coarse) of crush. Their own millers ensure a properly gapped mill, so that the brewer doesn’t have to worry about it. “We’re using the Rolls Royce of mills,” Lewis says (of a four-roller unit from Bühler Group, incidentally), “and the mill gap is checked every day with screens.”


Seismic Brewing checks mill performance with feeler gauges before every brew and sieve testing with an automated shaker on a regular basis.

Dialing It in for Better Beer

“There’s an opportunity for a lot of brewers to take a closer look [at their mills] and increase their efficiencies,” says Riley Aadland, application engineer at mill manufacturer RMS Brewing Solutions. Aadland is sympathetic to the sometimes-difficult calculus of whether to buy a mill or use pre-milled offerings. There’s more to consider than just the machine that cracks the kernel. “Malt handling is kind of overlooked, but it’s a necessary consideration,” he says. How grain is delivered and stored, how it is introduced to the mill, and what happens next are all variables (see “Overlooked Facets of Milling,” page 46). Space and other facility concerns can quickly complicate the equation.

Fifty miles north of Pond Farm, in Santa Rosa, California, Andy Hooper takes milling seriously. Seismic Brewing is a three-year-old production brewery with a 60-barrel brewhouse built to make 40,000 barrels annually. The brewery focuses on sustainability as well as growth; a key element is sourcing local ingredients.

“We use a lot of California-grown malt,” he says. “It’s more expensive than Rahr, and I want to taste that in the beer.” One of their tools for unlocking the flavor potential of craft malt is their mill—a German Künzel four-roller mill with internal sieve (which helps keep the crush size uniform and the hulls more whole). Another is the brewery’s detailed standard operating procedures.


“Many U.S. craft brewers focus on hops over malt,” Hooper says, “and they’re happy to sacrifice efficiency for [lautering] speed. A couple of bucks of malt makes up the difference in extract, and it’s a smart tactical business decision to not micromanage the mill.”

But the fine character he’s after in Seismic’s beers necessitates diving into the details. That means using a set of sieves on “a very regular basis,” checking the mill gap with a set of feeler gauges for every brew, and recording all this data for recall later on. Hooper even uses an automated shaker to remove the variable of different brewers performing the test. “It’s a culture thing,” he says. “The whole team takes data and analysis seriously. Sometimes it’s borderline too much, but we’re all striving for quality.”

A few miles down the road from Seismic is the famed Russian River brewpub. Still there is a two-roller mill that came with the brewhouse Vinnie Cilurzo bought when he built out the brewpub. It’s still in use today for some of the pub-only beers, but Cilurzo hopes to replace it with a four-roll mill in the future. “This won’t match the wet mill, but it will get it closer,” he says.

The production brewery’s wet mill is only part of the picture that led to higher efficiencies, drier beers, and a “softness” of which Cilurzo is proud. He credits the malt-cleaning equipment for the improvements, and the system vacuums away grain dust and small particles while an optical destoner removes any non-grain debris. Any pebbles caught by the destoner are ejected into a bin beside the mill.


“I’m flabbergasted by how many stones get removed,” Cilurzo says. He says he hopes to one day pave a walkway on the brewery grounds with the rocks and dedicate it to his malt suppliers. The wet mill itself treats the malt more gently, leading to fewer polyphenols and higher wort fermentability. “We work really hard not to beat up the malt while moving it around the brewery,” Cilurzo says.

John Barleycorn, with his heroic cache of sugars and enzymes held within a fibrous husk, is the perfect grain for brewing. Thousands of years after we crushed the first kernels, humans are still developing better ways to unlock their treasures. Maybe the miller is not the villain of the song after all, but the helpful artisan who facilitates John’s transformation from abused cereal to lauded libation.

So, next time you’re done milling in, raise a toast to John Barleycorn and the machines that unleash his potential.


Russian River's T-Rex wet mil.

Overlooked Facets of Milling

How malt moves through the brewery is an important aspect to the greater malt-handling system. Typical solutions are the common and less expensive flexible auger types, and the more complex puck-and-chain types. Flex augers can be rough on the grain, breaking kernels and making more dust and chaff, and it can be difficult to route them in a brewery, since they’re limited to a roughly 45-degree angle when raising grain. (Thus, the mill must be placed at least as far from the mash tun or grist case as the difference in height between them.) The chain discs, meanwhile, use a moving array of flat pucks to carry the malt and are gentler on the grain. They are more expensive and require more maintenance, but they can move grain almost vertically and turn corners.


Sieving grist is the common method of measuring a mill’s output. How it works: Add a weighed sample of the grist to a stack of pans with screens of a prescribed gauge and agitate. The screens capture various particle sizes, with the coarsest remaining in the top pan and the finest flour falling to the bottom pan. It is then possible to weigh out a ratio of coarse/fine/flour and compare it to the target (often included on the malt spec sheet provided with each lot). The American Society of Brewing Chemists has detailed procedures and specifications for performing the tests. While those are considered best practices, they are far from standard operating procedure at most breweries. It’s rare to find a brewery that owns a set of the inexpensive tools, let alone one that uses them regularly. It’s a fiddly, labor-intensive process that most brewers forgo in favor of a visual inspection and empirical analysis of how the grist performs in a mash.

The Hammer Mill
There’s another type of mill that’s the most efficient of the bunch, but it is most often found in large industrial breweries. The hammer mill uses spinning sledges to pulverize the grist into a fine flour. Grain milled in this way would be extremely difficult to lauter, except that it’s usually paired with a mash filter instead of the more common mash tun. For more on mash filters, see:

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