How to Mill Grain for Beer

Step 1

Set the gap with a feeler gauge, not the dial

Dial markings and detents on mills are indicative rather than accurate, particularly on budget models. Since the entire point of owning a mill is controlling a number precisely, measure it.

1. Get an automotive feeler gauge set. They cost very little and have leaves in thousandths of an inch.
2. Slide the leaf you want between the rollers and adjust until it is a firm but sliding fit.
3. Check both ends. If your mill only adjusts at one end, the gap will be wedge-shaped and one side over-crushes while the other under-crushes.
4. Mark or note the setting so you can return to it.

Start at 0.035 inches if you are unsure. The numbers for different processes are in grain mill gap settings.

Step 2

Run it slowly. This is the big one.

The most common mistake in milling, and the one that causes stuck mashes and poor efficiency, is speed. A cordless drill at full speed spins mill rollers far faster than they are designed to turn, and the result is grain that gets shattered rather than crushed: flour instead of grits, and husk destroyed rather than opened.

• Hand crank is the gold standard. Ten to fifteen pounds is a few minutes of mild effort, and the speed is naturally low.
• Drill in low gear, well under 500 rpm. Feather the trigger rather than holding it wide open. It should sound like grinding, not screaming.
• Never an impact driver. It is the wrong tool in every respect.
• A geared motor if you mill in bulk. A slow, torquey motor is the right permanent answer and is the setup serious millers build.

Step 3

Judge the crush by looking at it

You do not need instruments. Take a handful from the bucket and look:

The target is simple to state: husks intact, endosperm broken. The husk is the filter bed your wort will drain through; the endosperm is what the enzymes need access to. A good crush separates the two without destroying either.

If you see lots of whole kernels, tighten the gap. If you see flour and shredded husk, either widen the gap or -- more likely -- slow the mill down.

Step 4

Consider conditioning the malt

A technique worth knowing, and genuinely useful for anyone milling tight. Conditioning means lightly misting the grain with water -- roughly 1 to 2 percent by weight -- and letting it rest for ten to twenty minutes before milling.

The water is absorbed by the husk, which is thin and permeable, and barely penetrates the endosperm in that time. A damp husk is pliable rather than brittle, so it survives the nip intact while the dry interior still shatters normally.

• Mist, do not soak. A spray bottle and a stir. Grain should look slightly dull, not wet.
• Rest 10 to 20 minutes, stirring once. Longer and moisture reaches the endosperm, which makes it gummy rather than brittle.
• Mill immediately after the rest. Do not store conditioned grain -- damp malt spoils.
• Expect the mill to work harder. Pliable husk grips more. Run slower still.

Step 5

Mill fresh, and mill into something sensible

Crushed malt starts losing aroma within days and is noticeably stale within weeks, because you have broken the husk that was protecting it. That is half the reason to own a mill: buy whole grain in sacks, mill on brew day.

• Mill into a bucket with a lid, or straight into your mash tun. Not into an open tub in a dusty garage.
• Expect dust. Milling throws fine flour into the air. Mill outdoors or in a space you do not mind dusting, and consider a mask if you mill large quantities.
• Store whole grain cool, dry and sealed. Whole malt keeps for a year or more; crushed malt does not keep at all.
• Weigh before milling, not after. Some dust is always lost.