Motorize Your Grain Mill: Projects

Parts List

  • Sheave, 1/2” diameter x 1.5” $3.50
  • Sheave 1/2” x 10” $15.00
  • 1/2” x 44” L3 belt $7.00
  • Plywood for base $4.00
  • Plywood/MDF for grain hopper $2.00
  • Masonite for grain hopper $2.00
  • Bolts for grain mill $1.50
  • Screws for hopper and motor mount $2.25
  • Miscellaneous nails, screws, tape, glue $2.00

Although you can make a good pale ale, porter or wheat beer with an all-extract kit, most brewers use crushed grain in their brewing. Inevitably the urge to add “just a touch of something special” motivates brewers to steep specialty grains or even perform mini-mashes. That requires grain — malted, roasted, toasted, even raw.

Most homebrew shops, local and internet-based, will supply pre-crushed grain. However, like every agricultural product from peanuts to pomegranate, freshness is key. Recently crushed grain is more fresh.

So, you ask, how is grain crushed? The answer is, properly milled grain is squeezed, fractured and pressed into pieces by grooved plates (corn mill or burr-type mill) or rollers with a textured finish. Well crushed grain should have large pieces (halves and quarter kernels) with minimal amounts of flour and bits (slivers of grain).

According to Briess Malting, a good mill will separate the grain husk from the endosperm, leaving the husk relatively intact, then break the endosperm into several pieces instead of shattering it into small slivers and flour. An ideal distribution of size would have 80+% of the grain particles sized to a “14–30 mesh screen.” This means that if you dump your crushed grain into an ordinary wire kitchen colander, which has 14–30 holes per inch, 80% of the crushed grain should remain after some vigorous shaking. This is a good way to check both your own crush and your homebrew store’s.

“Excessive finer endosperm and husk particles create a compound challenge facing many small-scale breweries — lautering time,” says Briess Malting. In other words, too many fine particles gum up the works, slowing down the lauter and increasing leaching time for tannins and other harsh or astringent flavor notes.

Commercial brewers, many microbrewers and maltsters have large mills that use multiple pairs of rollers to crush grain. After each step the grain can be run through a sieve that separates smaller particles to prevent them from being crushed again. Home mills typically have one pair of rollers, though some use three rollers.

Why not just purchase grain pre-crushed from your local home brew shop? Three good reasons are: uncrushed grain is usually cheaper, crushing just before mashing provides maximum freshness and you can adjust crush for maximum yield and lautering (filtering the wort through the grain bed) in your system.

How to and why to

A common drill motor can motorize most mills. The problem with this approach is, while it works, it simply works too fast. Optimum roller speed for small homebrew mills is 150–200 rpm. Drills and most AC motors run at 1,750 rpm (U.S. 60 cycle AC.) The answer is to use pulleys and belts or an expensive gear reduction motor to run your mill more slowly.

Motors are ubiquitous. Cruise any neighborhood for a couple of weeks and you’ll undoubtedly find a salvageable 1/3 horsepower motor from a furnace, washer, dryer, dishwasher — the list is endless. I have at least three! A couple of pulleys and you’re almost there — but the trick is in the details.

If you’re starting from scratch, you’ll need to mount your new mill onto a supportive structure that will hold the mill and motor, construct a grain hopper of suitable capacity, and add pulleys and a belt. If you’ve been running your mill by hand or drill, we’ll show you how to add a proper motor.

Most mills can be mounted above or below their supporting platform; many manufacturers recommend positioning the mill below its support. This makes mounting the grain hopper easy, but slightly increases the complexity of fitting the large driven sheave. (Sheave is the correct terminology for what most of us call a pulley.)

Hand driven mills can be mounted to a plank and drop the crush directly into a bucket. A motorized or hand-driven mill can be mounted on a larger plank clamped to a table, with a bucket below the mill to collect crushed grain. Or you may want to create a stand-alone grinding station. That’s the option I chose — a simple stand that supports the mill and motor, with a bucket below.

If you already have a mill, you’ll have only a few steps to follow. First determine the speed of your motor. A few are slower than 1,750 rpm. Assuming your motor is 1,750 rpm, you need to calculate the correct input sheave diameter and driven wheel diameter. (See the following formula). Most of you will end up with a 1/2” (13 mm) x 1.5” (40 mm) drive sheave and a 1/2” x 10” (250 mm) driven sheave. Adaptors to increase 3/8” drive shafts to 1/2” are available so don’t give up because your mill came with a smaller input shaft.

To insure the slowest possible speed, I used a 1.5” input and a 10” driven sheave. Instead of the “proper” 4L V-belt (1/2” x 5/16”) I used a thinner 3L belt (3/8” x 7/32”.) Because the thinner belt rides lower in the pulley, I get a smaller effective drive of 1.05”, and the driven sheave is relatively unchanged at an apparent driven diameter of 9.55”. The result is that my mill runs at approximately 185–200 rpm.

The best way to calculate the correct drive and driven sheave diameters is to use charts published in Grainger and other industrial supply catalogs ( catalog), or this online calculator: calc.html.

Step by step to a proper malt mill

Step one: Make a support stand (if desired). Some of you will prefer to clamp the structure to a stout table (the complete assembly weighs approximately 40 lbs. or 18 kg.) I made a folding stand, an open “U” shape that sits tall enough to accommodate most buckets underneath the mill discharge. The stand has three “H” legs joined with hinges. To the under side of the mill platform I added 1” x 1” (25 mm x 25 mm) cleats. The completed “U” support wraps tightly against the cleats and the shorter legs are clamped to end cleats for extra rigidity.

Step two: Mount mill to a support structure. I made mine of plywood, 3/4” x 12” x 24” (20 mm x 305 mm x 610 mm) to allow room to mount the motor and hopper.

Step three: Cut a rectangle in the support base to pass grain to the mill. Mine is offset 1” (25 mm) from the side and measures 4.5” x 1.5” (120 mm x 40 mm.)

Step four: Mount the mill. I can’t give you locations; every mill is different. Drill larger holes than necessary to allow for adjustment. For my CrankandStein mill, I drilled 5/16” (8 mm) holes for 1/4” (6 mm) bolts. Use flat head bolts and washers to allow for mill adjustment. (I didn’t use them initially and encountered some binding of the rollers until I changed to flat head.)

Step five: Build a grain hopper. I used dimensions similar to the polyethylene container I use to haul up to 14 pounds (7 kg) of grain — that’s the maximum capacity of my mash tun. The hopper is 10” x 12” (250 mm x 300 mm) tall with 45° angles to funnel grain to the mill.

I first cut 3/4” (20 mm) plywood to size for sides, then two end pieces of thin masonite. To form the 45° angles was simple. I found the center of each sidepiece, measured 3/4” (20 mm) to each side of the center to form a 1.5” (40 mm) throat similar to the opening in the support base. Adding 1/2” x 1/2” (13 mm x 13 mm) cleats (supportive wooden blocks) on a 45° angle took moments. They’re screwed to the plywood and trimmed flush.

Finally I screwed both masonite ends to one side and hot glued both 6” x 8 3/4” pieces of masonite to the cleats. Then I screwed on the other side. This created a box with sloping sides that directs the grain into the mill. (It’s not perfect, almost 4” of floor remains exposed. I can live with that, or add another piece to complete the funnel.)

You’ll want to secure the hopper to the base board in some manner once you’re done with construction and have aligned all the pieces. I made mine removable by permanently attaching wooden blocks to two sides of the hopper and screwing those blocks to the base platform. When I need to clean or modify the hopper or mill I can conveniently remove the screws in seconds.

Step six: Attach the large driven sheave to the grain mill and the smaller sheave to the motor. Line them up accurately and secure the motor to the base plate. Most motors already have a carriage, if not they are available. Be sure to cut mounting slots, not holes, in the base so you can adjust belt tension as well as easily fit the belt.

Step seven: Measure the belt length. The easiest way to measure is to use a cloth measuring tape. My belt is 44” (117.6 cm) long.

Step eight: Attach the belt and apply tension to the motor. Do not make the belt overly tight; the belt must be able to slip should the mill’s rollers get jammed. My mill requires a clockwise rotation; the motor is mounted to provide this rotation. Check your motor’s rotation and mill’s requirement.

Step nine: Make a belt guard. Do not neglect this step. If your finger gets caught between the belt and sheave you are quite likely to suffer an amputation. I made a belt guard out of scrap masonite 21/2” x 20” and scrap 3/4″ x 1 1/2″ board. It is basically an “L” shape and attaches to the grain hopper with screws. The 2 1/2 ” lip extends over the driven wheel and the drive sheave.

With all construction completed, disassemble the mechanical parts and seal, then paint or varnish the wooden surfaces to protect them. Reassemble, take a picture and send it to BYO to share! (Send us a beer, too, while you’re at it!)