Malt or grain handling is a line item that most brewers rely on others to advise them on, but with a bit of basic knowledge, any brewery owner or brewhouse planner can take a more active roll in designing and developing their own malt-handling systems. While most very reputable brewhouse and tank-equipment providers’ intentions are good, there are many common mistakes that every brewery professional in a design phase should be aware of in order to avoid costly change orders and redesigns down the road.
Measure the right thing
The most basic oversight is one of the most simple to correct—the volumes specified for most grain-handling equipment are for whole-grain kernels; once the grains are rolled through the mill, the grist created is less dense. Grist is about 30 percent less dense than unmilled grain kernels, so any system planning should account for that lower density of milled grain and not the high density of whole kernels.
Auger Sizing and Calculations
So let’s dive in to our first calculation. A 3" flex auger is rated for 50 pounds per minute—for whole kernels. This calculation works for pre-milled grain, such as from silo to specialty hopper and specialty hopper to the top of the mill.
Post-mill grist will transport through a 3" flex auger at a rate of 35 pounds per minute—a figure that accounts for that 30 percent lower density.
If you take anything away from this article, this should be it—many manufacturers’ auger rates for post-milled grains fail to take the reduced density of grist into consideration, so a specification on a sheet may seem appropriate for your brewery build, but reality will come in the form of long mash-in rates, especially for heavy grain bill loads.
Instead, consider using these parameters to size a proper grain-handling system. Target your mash-in rate at 30 minutes max and roughly calculate your grain conveyance at 1,000 pounds per barrel brewhouse capacity. So, for example, a 15 bbl brewhouse calculates out to 1,500 lb of mash grist with the goal to mash in at 30 minutes or less. A 3" auger (at 35 lb/min) would be short of that target mash-in (35 lb/min x 30 min = 1,050 lb). In that case, you would specify the next auger size up and calculate out the feed rate taking the grist load into consideration.
Grist-Case Sizing and Configuration
A cubic foot of whole barley weighs about 36 lb. A cubic foot of grist weighs about 25 lb, but it occupies the same physical space. Grist cases are often sized based on the space requirements of more dense whole kernels and not your less-dense grist. Again, you need to take the fluffiness of cracked grain into account. A “2,000 lb” feed grain hopper is really a 1,400 lb grist case (70 percent of 2,000 lb is 1,400 lb). But that’s not where the story ends.
Another physical reality that is often overlooked is the angle of repose of the grain. To explain, when grist from the mill enters the grist case, it settles in a cone with a 30° angle at the base. This forms an upside-down cone that does not settle out flat. Space needs to be accounted for to make room for the cone; otherwise your grist will back up into your mill, and that is no fun. The calculations are more complex and outside of the scope of this article, but for more resources on formulating and calculating grist-case volume with the angle of repose, please visit HRVST.com.
The simple take-away is that grist, or post-milled grain kernels, is about 30 percent less dense than whole-grain kernels, and target mash-in time should be 30 minutes or less. Grain also forms a cone when it enters the grist case and doesn’t settle flat like liquid, so the added volume of that cone angle needs to be taken into consideration when sizing the grist case. If you’re currently in the design phase of a brewhouse build-out or expansion, your best bet is to consult a grain-handling specialist for your grain-handling needs rather than simply relying on a turnkey brewhouse package that includes grain-handling components. But if a package deal makes more sense for economic or logistical reasons, consider the parameters here and ask the right questions to make sure what you specify can handle the needs of your brewhouse.