Wet milling remains one of those topics that brewers discuss but rarely encounter in the wild. Once solely the province of the largest craft brewers, in more recent years wet mills have become slightly more common but remain unusual to find in a smaller craft brewery.
In contrast to dry milling, wet mills steep malt in a continuous stream of warm water to allow the grain’s moisture level to rise to a set mark, usually 15 to 20 percent. When a wet mill’s rollers grind the malt, the grain’s husk remains intact and doesn’t fragment. This significantly reduces the amount of dust and debris created and allows for faster run-off time and more loading of the lauter tun. The downsides, beyond cost, include additional cleaning of the mill and its rollers along with an increase in the time required to mill the malt.
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We recently spoke with Scott Shirley, the Director of Brewing Operations at Lawson’s Finest Liquids in Vermont, to learn more about his brewery’s experience with a wet mill and hear what advice he has for brewers considering one.
Deciding On A Wet Mill
When he was looking to build out a new brewery, owner and founder Sean Lawson decided to go with a wet mill to grind malts for his finest liquids. Two of the reasons were straightforward: space was at a premium in the brewhouse and cellar and the local wastewater system was a challenge. Scott Shirley joined Lawson’s in 2018, shortly after construction of the new brewery in rural Waitsfield, Vermont, and his experience with his first wet mill began.
“We’re a little bit hamstrung by our wastewater system,” Shirley notes. “So we want to get as much out of the grain with as little waste as possible, that was really a big goal.”
Beyond that, the GEA wet milling system fits into a small footprint, according to Shirley. “It’s not much more than four, maybe six square feet, that it sits on. So it fits very well in the configuration that we have. The footprint of it really was attractive.” The grist case is stacked on top of the mill, which employs two 12 to 14 inch rollers.
The Absence of Dust
One of the biggest benefits of a wet mill system is the reduction and near elimination of grain dust. “It’s super clean,” Shirley says. “There’s no dust, so in a small, confined space of the facility that we’re in here, we don’t have to have an isolated room for a mill and dust collection and all the problems with that. So that’s certainly a nice benefit to this system.”
One of the strongest points in favor of the wet mill is the efficiency boost it gives. “The ability to be able to crush the grain finer than we normally would, because we’re keeping the husk intact during the steeping process, looking at our brew house yields, I would say we’re probably, at our regular gravity beer of 12 Plato, we’re somewhere in the 96 to 98 percent extraction rate,” Shirley says. “So, really good. When we’re making our Pilsner, sometimes I see that number at 100 percent.”
Trade-offs and Downsides
In contrast to dry mill systems, the wet mill will slow down the mash-in process. Shirley and his team have to mill the grain as they go and there are limits on how much grain the system can handle at a time. “It takes longer to mill the grain than it does to mash in typically,” Shirley says. “It adds time to the mash-in process, because you’re doing it all at once, you’re milling the grain and mashing in together. So that part is a little slower.”
But the time lost during mashing in is regained during run off, Shirley says. “With that extract being 96 or 98 percent, our run off time is very normal,” he says. “To do that on a regular two or four roller dry mill and get that type of extraction, you’re going to have some really tough runoff, you’re going to be there well over two hours to get that type of extraction. And we’re well under two hours to get that. So I think you’ve gained back time and gained back efficiency.”
Shirley also notes that Lawson’s wet mill system doesn’t always play nice with certain types of specialty malts. In brewing Lawson’s popular Big Hoppy Black IPA this past fall, Shirley and his team ran into some issues with the darker malts in the wet mill. “It had some carafa malt in it and the wet mill did not like it,” Shirley laughs. “Because they’re dark roasted malts and barleys that are higher in protein, they were sticking to the roller. They were causing some really long runs.” He notes this problem was unusual for them and he hasn’t heard of others having an issue with these darker malts.
The wet mill also requires greater attention to details such as monitoring the water to grain concentration in order to avoid the system getting dry and clumpy. He also recommends regular cleaning of the wet mill with caustic (and not acid) to avoid protein buildup. His team cleans the system every two weeks.
Weighing The Pros and Cons
“I would look at it in terms of ROI,” Shirley advises. “What’s your return on getting that extra couple of percentage points? Are you going through enough grain to upgrade to that system? For us, the footprint of it really was attractive. It’s a pretty tight facility. So if you’re able to go high and tie that all into a small footprint, and not having to isolate a room and have dust collection and all that stuff, that can be