Overview of a Homebrew Grain Mill
Homebrew grain mills have a simple job, to crush the grains of malt in preparation for brewing. That being said, milling grain for home brewing is a little more complicated than that.
What a Grain Mill Does
What you want the grain mill to do is remove the husk and break the kernel (the endosperm) into just enough pieces to extract all the sugar. Of course, there is a trade-off. The finer you crush the kernel, the better the extraction and efficiency. But the finer you crush the kernel, the more “flour” you get as well.
Why Milling Too Fine is Bad
Have you ever mixed flour and water as a kid to make glue? Imagine what you get in your mash tun when you mill your grain too finely and produce a lot of flour… The sweet wort has to flow through the grain bed and out into the kettle, a process known as lautering. The process of adding hot water to the top of the grain bed to rinse the grains as we lauter is called sparging.
What we want is for the whole process to be continuous, ie. We do not want the rinsing and draining to stop suddenly because the liquid can’t flow through the sticky grain bed. This is what we call a stuck sparge.
How the Husks Help Filter the Wort
It’s the grain husks that act as a filter medium and keep the whole thing moving along. We want the husks to be as intact as possible, not only for filtering, but also because finely shredded husks can cause astringent off flavors due to tannin extraction.
So, you can see where something simple like crushing your grain with a homebrew grain mill can get complicated when we start talking about efficiency and stuck sparges.
Every System is Different
I believe what you will find is that every homebrew system handles the grist differently during the mash and lautering. This all has to do with the diameter of the Mash/Lauter Tun (MLT), the design of the false bottom or screen used, the diameter of the drain hose and size of the valve on the MLT, and how the liquid gets from the MLT into the drain line. One system may get stuck sparges often and another may never get stuck sparges at all.
Related: Learn How to Brew in a Bag
Types of Homebrew Grain Mills
When it comes to homebrew grain mills, home brewers primarily use two types, the Corona (and Victoria) Mill with burr grinders and the roller mill, which of course uses rollers to crush the grain.
Each homebrew grain mill has pros and cons and you can find all kinds of information on modifying the Corona and Victoria Burr Mills to do a better job. But, for most homebrewers, it is well worth the money to purchase a quality roller mill. There are a lot of brands on the market but the one I recommend, and the one I use, is The Barley Crusher MaltMill. Why? Because of the quality of materials, the cost-effectiveness, and the quality of the end product, your crushed grist. Check out the manufacturer’s website here.
- 【Large 7.7LB Hopper】 : Upgrade thicker hopper can hold up to 7.7 lb grains at one time. Large capacity for you to handle large batches of brewing. Especially designed for malt, barley, and wheat, not recommend for corns and soybeans.
- 【Powerful Knurls & Adjustable Gap】: 5-inch rollers, 12 TPI knurl, efficiently pulls all your grains through while leaving the hull intact to form an excellent filter bed for sparging. The clearance of two rollers is adjustable to acquire your desired fineness from 0.025 to 0.1 inch. A great helper for homebrew!
- 【Strong Drill Mode】: Attach an electric drill and give your arm a rest! Give a throughput of 7 pounds in just one minute drill mode! much more powerful than traditional manual mode. (3/8 inch, low speed drill) If you're brewing large batches, or want to maximize mash efficiency, you should definitely try the drill mode!
Getting into a debate on the different homebrew grain mills is better left for another article. Everyone has their own favorite. I’m pretty frugal so I like the Barley Crusher MaltMill and I use a 3/8” drill I bought at Harbor Freight to power the mill. I generally keep my gap at 0.032″-0.036” or (0.8636mm-0.9144mm) but depending on the type of grain I’m using, I may have to make slight adjustments real-time.
- Feeler gauge set: made of 65 manganese steel, each measuring feeler gauge has 32 blades thickness; Foldable feeler gauges, easy and convenient to take and store
- Easy identification: dual marked metric and imperial, 0.0015 inch/ 0.04 mm to 0.035 inch/ 0.88 mm, the numbers of size are etched into feeler gauge for easy identification
- Metric sizes (mm): 0.04, 0.05, 0.06, 0.08, 0.10, 0.13, 0.15, 0.18, 0.20, 0.23, 0.25, 0.25, 0.28, 0.30, 0.33, 0.35, 0.38, 0.40, 0.43, 0.45, 0.48, 0.50, 0.53, 0.55, 0.58, 0.60, 0.63, 0.65, 0.70, 0.75, 0.80, 0.88
I use a gap wrench to make the adjustment, just tighten the rollers until the wrench is snug but pulls out with a little effort.
Being that some people are more “visual” than others, I’ve got some images of “Good”, “Bad” and “Ugly” grist:
A Good Crush
As discussed above, a good crush is one that produces little flour, breaks the kernels apart, and does not shred the husks. Take a look at the images above. All three images show what a good job of milling your grain should look like.
A Bad Crush-Too Coarse
This crush is bad because too many grains are left intact. How will you know if your crush is too coarse? When you examine the grist, you will not see many husks or broken white pieces of endosperm, but you will see too many whole unaltered grains of malt. If you didn’t catch it in time, low efficiency is a good indicator.
An Ugly Crush-Too Fine with Too Much Flour
This is a bad crush because of the amount of flour produced and because of the shredded husks. How will you know if you have crushed your grain too finely? You will notice a lot of flour in the grist, the pieces of broken endosperm will be very small, and you will often notice that the husks have been shredded as well. If you didn’t catch it in time (and there is not much you can do about it other than add rice hulls to the grist), you will know you have milled your malt too fine if you end up with a stuck sparge. It is possible to mill too fine and not get a stuck sparge but have your beer develop astringent off flavors from tannin extraction of the shredded husks.
So, in conclusion, you may have to experiment a while on the homebrew grain mill you use and your system until you find the perfect crush that works best for you.
- always mill outside to keep the dust down
- mill just before you brew to minimize oxidation of the grain
- use rice hulls when you are unsure of your crush, especially when using a lot of wheat
- purchase the best homebrew grain mill you can afford along with a drill to power it
- if there is a hopper add-on available, purchase it when you order your mill, you will thank me later
- if you are handy, build a stable table to mount your homebrew grain mill on with a way to stabilize the drill (if you use one and not a motor)
- on my Barley Crusher Maltmill, when the rollers won’t grab the grain, I sometimes run a thin knife across the gap…this either removes an obstruction
or forces grain into the gap…I’m not sure which but it works more times than not
- keep your gap gauge in a nice dry place with a light coat of oil…they rust easily
- check your crush as you go and adjust the gap if needed…don’t wait until you’ve finished and it’s too late
- I read in an old brewing primer from 1760 that milling your malt heats it up and reduces the mash efficiency…not sure if this is true but you might want to make a habit of giving the milled grist a little while to cool before you dough-in, just in case