All-Grain Brew Day Walkthrough (II: Milling)


A two-roll homebrew grain mill, with some malt in the hopper.

This is the second installment in the All-Grain Brew Day Walkthough, which started with a post on strike water preparation

Once your brewing liquor has been made, tasted, and is being heated towards strike temperature, it’s time to turn your focus to your grist. The first thing you should do is take a few kernels of your base malt and chew them. Most importantly, ensure that the malt has not gone stale. Secondarily, note any impressions you have of the flavor or aroma. If you’re new to brewing, you may find it hard to describe what you are sensing, but you will get better when you have other malts to use for comparison.

You may also want to chew a few grains of the lighter specialty malts, such as crystal malts. Darkly-roasted grains — such as chocolate malt or black malt — are much harder and often very bitter when tasted alone. I usually just smell them to see if their aroma is good.

Record your observations in your brewing notebook or brewing software, and it’s time to mill the grain.

The grain mills used by homebrewers, and homebrew shops, are mostly two-roll mills. These work fine when milling well-modified malt, which most homebrew is made from. (Commercial breweries, especially those who use less-modified malts, tend to use four- or six-roll mills.) Homebrew mills can be hand-cranked, but are frequently powered by a hand-held drill or less commonly by a “motor, belt, and pulley” setup.


Pre-Milled Grain and Fixed Gap Mills

If your grain was pre-milled, proceed to mashing in. If you have a grain mill with a fixed mill gap— in other words, you can’t adjust the space between the rollers — mill your grain. After milling, check the quality of your crush. It’s hard to describe what a good crush looks like, and it’s even hard to illustrate with photographs. A good rule of thumb is that every kernel should be cracked and most of the husks should be split into three pieces. About one third of the starch should be in the form of fairly large grits, another third ground into flour and the remaining third intermediate between these two. If you think your grind looks too coarse, run the grist through the mill again.


Adjustable Grain Mills


This spark plug feeler gauge can tell you what your mill gap is.

If you have an adjustable grain mill, you have a few options when it comes to milling. If the kernels of your malts are all approximately the same size, just mill them together. Set your mill gap to a width that looks reasonable and mill a handful or two of malt. Examine the crush to see if it looks satisfactory. You can do this visually, or if you want to go nuts, use standard sieves to evaluate the crush. (However, I don’t know any homebrewer who does this; even most brewpubs don’t.)

Adjust the mill, if needed, and repeat until you get a crush you’re satisfied with, then run the remaining grist through the mill. If you want to know the width of your mill gap — perhaps to record in your brewing notebook for future reference — use a spark plug feeler gauge. These are available at any auto supply store. The gauges are a collection of thin metal plates of known thickness. This value is written on each plate. Find a combination of plates that just barely fits into your mill gap and add up the widths. A good “one size fits all” mill gap for two-roll mills is 0.035–0.050 inches (0.89–1.3 mm).

If you are milling malts with different sized kernels, you might want to mill them separately. That way, you can adjust your mill gap to suit each malt. Many homebrewers will mill their dark grains separately when making a stout, porter or other dark beer. Sometimes the grains are milled very finely. Additionally these finally milled grains are sometimes withheld at mash in and only stirred into the top of the grain bed near the end of the mash.

The big tradeoff in milling is extract efficiency vs. ease of lautering. Homebrewers chasing extract efficiency typically start with middle-of-the-road crushes, then crush their malts more finely each subsequent brew day. When they finally encounter lautering problems in a batch, they back off a notch.


Malt Conditioning


Sieving with standard sieves can provide a more quantitative assessment your milling.

One final option to consider when milling your grain is malt conditioning. The idea behind malt conditioning is that the grain is lightly wetted immediately prior to milling. This makes a the husks more pliable, so they break into fewer pieces when milled. As a consequence, you can tighten your mill gap and get smaller grits from the endosperm of the malt and still have large enough husk fragments to aid in lautering. This raises your extract efficiency and in addition, you get less tannin extraction than if you dry milled your grain to yield the same consistency of grits. (This would, of course, coincide with much smaller husk pieces.) In a previous article, I described one way to condition your malt at home. Basically, you steam your malt briefly in your lauter tun. The heat steam is quickly absorbed into the husks (but doesn’t make it to the endosperm). The malt should be milled immediately after steaming. This requires a lauter tun that can be heated.

Malt conditioning is one form of wet milling, but there are others. Most malt milled in breweries, whether homebrew or commercial, is dry milled.

Next up, mashing in.


Related articles

Porter (Dark Grains in the Brewhouse)

Assess Your Ingredients (Malt and Water)

“Freya’s” Eyes Golden Ale


  1. Andrew Debenham says

    I just read your article about conditioning malt by steaming it in your mash tun. I was wondering if this makes it any harder to clean your mill after the crush? I hadn’t heard about this so I’m thinking of trying it out on my next batch.

    • Chris Colby says

      If you do it correctly, the steam turns the brittle husks sort of leathery, but that’s it. You can run this steamed malt through your mill with no problem. (If a little “gunk” clings to the rollers, run a handful of dry malt through a couple times and that ought to take care of it.)
      If the malt starts gumming up the rollers, it has absorbed too much water. Keep the contact time with the steam short. (The duration is so short, it’s tempting to want to go longer.)

  2. I have spark plug feeler gauges for my mill, but A) they’re a bit of a pain to use and B) I don’t like the oil they’re coated in to touch my mill.

    My solution – a guitar pick. Dunlop Tortex green picks are 0.88mm, which is perfect for me (I brew BIAB and prefer a finer crush). When the pick goes through with just a little resistance, then I know my rollers are set to the right gap. If you want a wider gap, the blue ones are 1.0mm and the purple ones are 1.14mm. You can get a small pack of them at your local music store for a few bucks, and they’re not covered in mineral oil.

    • Chris Colby says

      A guitar pick! That is an awesome idea! They are almost always labelled with their thickness and in the right range.

  3. I use an old magic mill stone mill for my grains and I have found that if I put them in a bucket and use a spray bottle to mist them thoroughly about an hour before I mill, the crush is as good as any I’ve seen from a roller mill. I have never had any problem with astringency and my efficiency is usually around 80%. I have tried milling them immediately and for my setup it seems to work best if the husk has a chance to absorb the moisture.

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