Mill Your Own Grain

Whether you’re all-grain or partial mash brewing or just steeping specialty grains, you’ll find that selecting, milling, and using grain has its rewards. Here are some things you should know about milling grain.

What the Mill Does

For an efficient mash the grain must be physically crushed and broken apart. The resulting ground meal is called grist. It might seem as if the finer the grist the better, but when the mash is complete the grain has to be separated from the mash liquid. If the grain were ground to flour, separation would be difficult because nothing would flow through the grain bed.

The ideal grain mill breaks the grain into enough pieces so all the contents of every seed can be extracted and converted into simpler compounds during mashing. It leaves the husks as unbroken as possible. If the husks are left intact, they help keep the ground meal, or endosperm, separated enough to allow flow through the grain bed. The idea is to literally squeeze the malt until it’s crushed inside the husk, not to roll it like wheat in a bakery grist mill.

If you’re doing a partial mash of a pound or two of grain so that it’s fairly easy to separate the mash liquid from the grain using a grain (straining) bag, or if you’re just planning to steep specialty grains to add color, flavor, and aroma to an extract brew, the way the grain is milled isn’t too important. A good crush becomes a factor when brewing all-grain, where 10 pounds of grain can become a real mess if you can’t get the mash to flow through it.

Some commercial breweries add rice hulls or oat husks to the mash to help keep the grain bed light and fluffy, especially when using huskless wheat malt. For the average-gravity, five-gallon batch of all-grain beer, almost any crush will work just fine if the grain hasn’t been reduced to flour.

How Mills Work

Huge industrial malt mills have evolved to give a balance between the cost of mill operation and maintenance and the efficiency of the brewing process that results from the mill’s use. The main feature shared by almost all mills, whether designed for use by Anheuser-Busch or by you at home, is the use of pairs of parallel metal rollers.

Whether the rollers are a foot in diameter and four feet long or an inch in diameter and six inches long, the idea is basically the same. The rollers are held parallel in a frame, with a spacing between them that is small enough so no grain can pass between the rollers uncrushed.

Industrial mills may use two or three pairs of smooth rollers, each pair spaced differently for each stage of the milling process. Such mills also use screens, conveyors, scrapers, and other design features to separate coarse grist from flour and all grist from the husks.

As you’d expect, the industrial brewing giants have to get the most from their malt. Pennies count when you’re making 50 barrels of beer a minute, and big mill designs make economy and throughput top priorities.

A Mill for You

Of course, you and your local supply shop would like a mill costing less than a Malibu beach house. Over the years several manufacturers have built a variety of mills using the two-roller concept. One mill used a single roller held close to a flat, fixed plate, and another popular mill uses two rollers that are puposely not quite parallel.

Other differences between the various designs include roller size and materials, bearing materials, and grain-hopper size.

Mills priced in the $70 to $160 range are available from several manufacturers. When purchasing a mill, you should look for one that will treat the grain gently. When the rollers of the professional-size mills are reduced to homebrew size, they lose some of their ability to pull in grain smoothly and crush grain in stages. Watch out for homebrew mills that automatically grind the grain too fine.

Mill Motorization

The first thing that comes to mind after milling 15 pounds of grain using any hand-operated mill is, “Let’s motorize it.”

Although few manufacturers will actually recommend motorizing their mills, you should ask them if they feel their products can be safely motorized and if they will recommend the best way to do it.

The next thing that should come to mind is safety. Some mills can be easily powered in minutes by simply removing the hand crank from the drive roller and putting an electric drill on the drive roller axle. Most drills with 3/8-inch chucks can be used this way, but there are a few details to think about to avoid damaging the mill or yourself.

First, malt contains some debris. Grain that’s been swept up off the floor can contain small stones, for example, and these can get into your mill. When they do, they get crushed, something breaks, or the mill stops cold. In industrial equipment where heavy rotating components such as flywheels are mounted on shafts, the two are often keyed together with a soft metal pin. If something causes the shaft to lock up, the flywheel shears the pin and continues to turn rather than breaking the shaft.

You can mimick the shear pin by wrapping a strip of plain paper over the shaft of the drive roller, then putting the wrapped shaft in the drill chuck. Tighten the chuck by hand (not by wrench) just enough to turn the mill when fully loaded. If anything locks up the mill, the drill chuck will slip on the roller shaft.

Also, be aware of the huge difference in the available torque of various electric drills. Some expensive industrial drills produce enough torque to seriously hurt you if something brings them to a sudden stop.

When adding motors, power tools, and electricity to the brewing process, you need to think safety for yourself and others. An electric drill left plugged in and lying on the floor may be a minor threat to young children; a motorized grain mill left plugged in and mounted at bucket height may be a serious hazard. Think about what you’re doing and about what happens when fingers or clothing get caught in gear-driven machinery. Because brewing usually means water, pay careful attention when using a motorized mill.

When grain is milled in bulk using a powered mill, a tremendous amount of grain dust can be generated. Besides the risk of contamination of your beer caused by uncontrolled dust, a cloud of dust in the air can be a serious explosion hazard. Try to ventilate the milling area if you’re generating a good deal of dust, and avoid flames or sparks. This may not be a real problem for the average amateur brewer, but don’t take chances.

Milling the Grain

If your supply shop already has a mill set up for customer use, then you’re a very lucky brewer. Some stores have poorly mounted Corona mills that may be worn and difficult to handle or inconveniently located in high-traffic areas. Other stores may have permanently mounted, motorized roller mills set up directly under the grain scales. Either way, you’ll have to decide whether you want to use the set-up at the store or buy a mill for yourself at home.

To get the most from any mill, mount it in a convenient location. Some mills are designed to be clamped to a workbench, and others are made to sit on top of a five-gallon plastic bucket. In either case a sturdy set-up that allows one-handed operation of the mill is ideal. Workbenches and tables can be modified easily to both support the mill and to allow the grist to fall directly into a receiving bucket underneath.

An important point to always remember: Mill your grain in a location as far as possible from where you’ll be chilling your wort and fermenting it. Grain dust is rich in bacteria – bacteria that can contaminate beer quite easily.

You may have noticed in brewpubs and microbreweries that the grain storage and milling room is usually separated and sealed off from the brewing room. Often the grain is milled, mashed in, and piped directly into the mash tun. At home, don’t mill the grain anywhere near the kettle in which you’ll be chilling your wort.

If you choose to buy a mill for use at home, you may also want to think about the extra cost of scales for weighing bulk grain. You can weigh out whole grain at your supply store and mill it at home, but you may want to buy enough grain for several batches of beer and mill it as needed.

An alternative is to use emptied coffee cans of various sizes, measuring your large grain bills by volume. This is actually a good thing. Grain weight changes with moisture content, and measuring by volume from a calibrated container ensures consistent grain quantity from batch to batch. Just fill each of your various containers with grain and weigh the contents using any scale available, marking the weight capacity on the can itself.

Most homebrew supply stores have ample containers for use by grain brewers to measure grain and to store crushed malt temporarily. When purchasing grain for a single batch, all the grains can be weighed and poured into a single container. Then you can load the mill hopper from that container, milling the entire grain bill together.

After measuring out the malt using any convenient technique, pour the grain into the mill hopper. Some mills come with large-capacity hoppers that hold as much as six pounds of malt, and your store may have modified its mill to hold even larger amounts.

If the mill is motorized, start it up; otherwise, start cranking. Mill only the grain you’re going to use, if possible. This is like grinding coffee beans – the coffee stays freshest in bean form. If you mill too much and just can’t use it all, seal the remaining crushed grain in a large, plastic, food-storage bucket until it’s needed.

Try Before You Buy

If you’re ready to get into brewing from scratch or just want to put some specialty grains in a pot and add the tea to your extract beer, then you’re ready to try crushing some grain. Make a phone call or two, and find a supply shop that already has a mill set up for customer use. Find out what mill they’re using, and stop in and give it a try. Whether you mill at home or at the store, you’re sure to enjoy your beer even more after adding grain to the picture.

Issue: September 1996