Milling

File:Blue-milled-grain.jpg

Conditioned barley and wheat milled at 0.040" on a 3-roller mill

Grain (also called grist) consists mainly of starch granules (endosperm) inside a husk. Before the mash, it must be mechanically crushed using a grain mill in order to break open the husk and expose the starch and enzymes inside. The starch granules are also crushed in the process, increasing their surface area. In general, the crush quality affects the mashing process and saccharification time, lautering, efficiency, fermentation, and the color, taste, and overall character of the beer.

Basic Milling Process:

1. Set the desired mill gap.
2. Weigh out the grain on a scale per the recipe specifications.
3. Optional: Condition the grain. (See below)
4. Add the grain to the hopper.
5. Spin the drive roller to run the grain through the mill (into a bucket or directly into the mash tun). It's generally a good idea to visually inspect the crush after milling a handful of grain before continuing with the rest.

Grain Mills

Why own a mill?

• Freshness - Milling immediately before brewing results in the freshest malt possible (which is especially important when brewing to maintain fresh grain flavor).
• Control - Adjusting the gap and speed allows you to tailor the crush to your own system and maximize efficiency.
• Consistency - When other establishments mill your grain, the crush size may be inconsistent.
• Grain conditioning - Milling at home gives you the option to condition your grain. (See below)
• Cost savings - A mill will eventually pay for itself since you avoid a milling fee and you can buy grain in bulk.

The best mills available:

2-Roller Mills
Mill	Rollers	Bearing type	Accessories	Where to purchase
Cereal Killer, Kegco 2, Hullwrecker (All the same)	Knurled 1.25" x 5" hardened steel	Sealed ball bearings	Includes 7lb hopper, base, and hand crank	Amazon AIH Beverage Factory Austin Homebrew Supply Northern Brewer
Monster Mill 2	Knurled 1.5" x 6" hardened steel or stainless steel optional	Bronze bushings	11lb hopper, hopper extension, hand crank, and base are all optional.	MoreBeer (includes base and hopper) Monster Brewing
MattMill Kompakt	Fluted 2.75" x 2" hardened steel	Roller bearings	Hand crank and base are optional and hopper is generally DIY.	Austin Homebrew Supply
Malt Muncher 2	Knurled 1.25" x 5" hardened steel	Bronze bushings	Includes 6lb hopper and hand crank. Base is optional.	MoreBeer MoreBeer (Motorized) Amazon
3-Roller Mills
Mill	Rollers	Bearing type	Accessories	Where to purchase
Kegco 3	Knurled 1.5" x 6" hardened steel	Sealed ball bearings	Includes 11lb hopper, base, and hand crank.	Beverage Factory Amazon
Monster Mill 3	Knurled 1.5" x 6" hardened steel or stainless steel optional	Bronze bushings	11lb hopper, hopper extension, base, and hand crank are all optional.	MoreBeer (includes base and hopper) Amazon Monster Brewing
Malt Muncher 3	Knurled 1.25" x 5" hardened steel	Sealed ball bearings	Includes 12lb hopper and hand crank. Base is optional.	MoreBeer Amazon Brew Hardware
Premium Motorized Mills
Mill	Rollers	Bearing type	Accessories	Where to purchase
Ss Brewtech	Fluted 4" diameter stainless steel, with speed differential	Sealed ball bearings	Includes motor and 25lb hopper. Base/cart is optional.	MoreBeer
MoreBeer UltiMill	Knurled 2" diameter hardened steel	Undisclosed	Includes 60lb hopper with lid, motor, and stand.	MoreBeer

= Editor's Pick

Crankandstein has a couple of barebones offerings that are suited to the DYI homebrewer. You can get a basic mill and mount it in any mill housing design of your choice. They offer a 2-roller mill, 3-roller mill, and a 2-roller mill that can also crush corn. All of these have knurled hardened steel rollers and bronze bushings.

What NOT to buy
The "Barley Crusher" was intentionally excluded because it is a poor choice. It has soft rollers and soft/cheap bronze bushings, which lead to relatively frequent problems, and their customer service is sub-par. Lastly, other budget mills are available out in the wild, such as the motorized and 3-roller mills at Vevor. However, these cheap mills have bad reviews on Amazon and the specs look very suspicious, so we don't recommend them.

Some brewers use very low budget milling options such as food processors, rolling pins, or Corona/Victoria style disc mills (example from Amazon), but most likely you're better off buying your grain pre-milled if you're not ready to invest in a roller mill.

Features to consider

Knurled rollers on a 3-roller mill (bottom view)

• 3-roller vs 2-roller - The 3-roller works by pre-crushing the grain in the preliminary gap between the top two rollers, then opening the husk to expose the crushed kernel in the secondary gap with the third roller. The top gap is fixed at around 0.060" which easily pulls in both wheat and barley, softening the starch without tearing up the husk. The 3-roller mill provides less husk damage, which aids in lautering (among other things, see below). A 3-roller mill also more fully separates the starch from the husk, while providing superior grain feed. However, additional power (torque) is typically required to drive a 3-roller mill and they are generally more expensive.
• Bearings vs bushings - While higher cost, sealed ball bearings generally require no maintenance and have can a significantly longer lifespan than bushings, particularly if you drive the mill with a pulley or gears. On the other hand, bushings have more friction and may wear over time, such that they will need to be replaced at some point. Therefore we recommend a mill with sealed ball bearings. However, bushings are still generally OK when using a direct drive system such as a drill. Bushings may benefit from periodic cleaning and lubrication with a drop of food-grade mineral oil; check with the manufacturer.
• Roller material - For most brewers, hardened steel is the best option for roller material due to its durability. However, stainless steel has better protection against corrosion (although it is also more expensive). If you live in a damp or coastal region, stainless might be a good option.
• Roller diameter - Larger diameter helps the grain feed through the rollers. The biggest benefit from large rollers is that they allow a fluted morphology.
• Knurled vs fluted rollers - Roller morphology has an important effect on the crush and modern commercial mills always have fluted rollers. However, most home brew rollers typically have a diamond knurling pattern, which helps small diameter rollers feed grain through the gap. The relatively large diameter rollers on certain home brew mills (MattMill and Ss Brewtech) offset the reduced feeding ability from fluting. Therefore these large diameter fluted roller mills produce less damage to the husk while maintaining the ability to feed grain.
• Drive shaft - A 1/2" integrated drive shaft is the most durable.
• Hopper size - Hopper size is simply a matter of convenience and budget. It doesn't hurt anything if you need to pause partway through milling in order to fill the hopper with more grain, so larger hoppers generally aren't necessary. However, it is more convenient to add the grain to the hopper all at once, and some mills have optional hopper extensions to hold more grain. Portability, weight, and storage space should be also be taken into account in you are considering purchasing a hopper extension. It is also possible to make a hopper extension yourself.
• Throughput rate - Differences in roller length and/or how fast the rollers pull in grain is generally negligible for home brewers, and not something that needs to be considered. Throughput depends largely on milling speed and not the particular mill characteristics.

Gap Setting

0.049" dry crushing on a 3 roll at around 70 RPM, courtesy of Bilsch on LOB

All of the mills recommended here have an adjustable roller gap. Generally a smaller roller gap produces smaller grain particles.

The optimal mill gap setting is dependent on your mill, your brewing system, and other factors. Therefore there is not a one-size-fits-all gap setting. For some brewing systems, the husks must be disintegrated as little as possible during milling because they are required for lautering. For other brewing systems such as BIAB, the grain can be finely milled if desired. The ideal gap setting can even vary based on the particular batch or type of grain. The crush should be monitored every milling to ensure it is being properly crushed. It is important that you experiment with different settings and find out what works best for you. For each batch the objective is to find an acceptable middle ground between efficiency (yield), lautering effectiveness, and quality. Un-crushed kernels with fully intact husks represent a direct loss of efficiency, so brewers should avoid a roller gap so large (coarse crush) that it does not crush all the grain. In a normal sample, you will find no un-crushed kernels. A fine crush gives only a small increase in efficiency, but can cause a large increase in lauter time and difficulty. On 2-roller mills you will find a point at which the mill will stop feeding the grain if you close the gap too tightly.

Particle size plays an important role in the gelatinization process, which affects the mash results. Specifically, decreasing the mill gap increases the sugar concentrations during the mash and also reduces the time needed for mashing. However "your mileage may vary" depending on your system, process, and ingredients.

Measuring the gap
For most systems, a gap in the range of 0.025" to 0.050" (0.7–1.2mm) is appropriate. To measure this, we use a very inexpensive tool called a feeler gauge. This tool is a stack of metal pieces with different marked thicknesses, which you can insert into a gap to precisely measure it. To achieve gaps that are not the same thickness as a single blade, stack multiple blades together to add up to the gap you want to measure. If you have a 3-roller mill and a normal (straight) feeler gauge, it is best to measure the gap before assembly, otherwise the adjustable gap will be inaccessible. If for some reason you do not want to buy a feeler gauge, you could use a standard credit card to get close to a 0.030" (0.76mm) gap.

Quality feeler gauge on Amazon - Blades range from 0.001" to 0.040" (0.03mm to 1mm), and it can measure larger gaps by combining blades.

Gap settings marked by the adjustment knobs

Process:

1. Insert the gauge as you are adjusting the gap. The blades should go into the gap between the rollers with a minimum amount of force, and should not be crushed in the gap. Try to adjust the gap on both ends of the roller to be the same.
2. On mills with adjustment knobs you can mark an arrow on the knob, and then turn it to set the gap at different points and mark on the frame what the gap is at the corresponding knob position. This way you can repeat different gap settings without getting out your feeler gauge again. It would be wise to mark in increments of 0.005" from 0.025" to 0.055" (every 0.1mm).

Finding the right gap
For your first trial at milling you may have to make a best guess with regard to the gap setting. If you have no test sieves, a good option is to adjust the mill by carefully evaluating one-cup samples. Start with the stock gap setting, or about 0.045" (1.1mm). Keep tightening the gap until you no longer find any un-crushed kernels. The problem with the "eyeball" evaluation is that even a one-cup sample requires a lot of patience to pick through. However, this should result in an "ideal" crush size for a good balance between yield and lauterability.

Driving the Mill

Three options exist for powering the mill:

1. Hand crank
2. Electric drill
3. Electric non-drill motor

Any of these options can produce a good crush, so what you choose just depends on your preference and budget.

Warning: We do not recommend driving the mill with a hamster.

Using a drill
For most home brewers, a drill is the preferred method to drive a mill. It is generally easier to set up and more economical than using a non-drill motor, and significantly less laborious than hand cranking. Low RPM drills provide the best speed control and torque. We generally don't recommend using an external speed limiter (example) on a high RPM drill because they significantly reduce the torque. Affixing a zip tie or 2" tri-clamp to the trigger of a variable speed drill can help control and maintain a constant speed. A corded drill is generally more powerful than a cordless one, and will usually last longer. However cordless drills can also work well, and they are more convenient for tasks around the house. The one requirement to using a drill is that the drill chuck fits onto the mill drive shaft (which range from 3/8" to 1/2" [9-12mm]).

Drills with cords

• 1/2" 0-550 RPM VSR drills from Harbor Freight are tried and true, and are the most frequently recommended.
• Amazon 10A 1/2" 0-800 RPM
• Amazon 8A 1/2" 0-850 RPM proven here

Drills without cords

• Milwaukee cordless on Amazon

Caution: If you are holding the drill while milling, you must also hold down the base of the mill. Otherwise the torque may cause the mill to flip over, causing damage and/or injury.

Using a motor
Some brewers prefer using a dedicated non-drill motor.

See Motorizing a mill.

Reducing torque requirement
If your drill/motor is having issues with stalling, or you'd like to reduce the load on it in order to extend its life, or you are wanting an easier job of hand cranking, you can reduce the amount of torque needed to drive the mill by reducing the amount of grain feeding into the rollers. All you need to do is create and affix cardboard inserts into the bottom of the hopper.

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Milling speed
Anecdotally, milling speed on a home brew mill has more effect on a good crush (specifically the prevention of husk shredding) than the roller gap or grain conditioning. A lower speed produces more intact husks/hulls. However, published data from commercial mills (albeit with very different rollers than home brew mills) indicate that roller speed does not hugely affect the crush, but may actually increase starch damage, which results in faster extraction.

The consensus on the Low Oxygen Brewing forum seems to be that running the rollers at about 50–150 RPM provides a good crush while minimizing damage to the husks. Other online sources generally suggest higher rates... around 150–300 RPM, but they also acknowledge that slower is generally better, the lowest speed your drill or motor can run without stalling. It usually takes a little more torque to get the mill going than to keep it going, so you will have to give it some more power to start the mill, and then slow it down once you are milling. If your drive method is struggling with the torque needed to mill at low speed, a simple solution is to limit the amount of grain flowing into the rollers.

Roller speed differential
Modern professional mills have the rollers spinning at different speeds. This increases the effectiveness of the crush by shearing off the husk from the endosperm, which serves to increase yield while reducing husk damage. The only home brew mill with speed differential is from Ss Brewtech.

Mounting the Mill

It is important to set up the mill on a base to keep the frames aligned properly. If the frames aren't straight, the rollers may bind. As you are securing it to the base, make sure all the rollers spin freely.

Most mills either come with a base or have one available. These bases are typically designed to let the mill sit on top of a plastic bucket, and this setup is fine in most cases. However if you are adding a dedicated motor, it's probably a better idea to attach the mill to a larger base or table of some sort.

Any Monster Mill accessories like this base will work for the Kegco 3-roller mill.

Milling Considerations

There are many complexities to keep in mind.

Husk integrity
Pulverizing the whole malt into flour should be avoided. Barley cell walls contain beta-glucans which are directly related to viscosity and therefore the rate at which the wort can be extracted, whether recirculating or transferring to the kettle. Grinding the grain (and husk) to a flour will break down the cell walls and increase the viscosity of your wort, increasing the likelihood of the dreaded "stuck mash". We want the husks to be as intact as possible, not only for filtering, but also because finely shredded husks can cause astringent, bitter, or harsh off flavors. Excessive milling promotes the extraction and solubilization of undesirable compounds into the wort and beer, such as silicates, lipids, husk-derived tannins (phenolic compounds), and large-molecular proteins, which can cause excess formation of trub, deposits, color changes, hazes, and a shorter shelf life. To put this in perspective, approximately 70–80% of the total polyphenol content of beer comes from the malt husk; and its transfer to the wort is largely influenced by milling parameters.

Husk integrity can be improved by conditioning the grain, milling slowly, using a reasonably large mill gap, and by using a 3-roller mill (or the Ss Brewtech mill that has unique rollers).

The professional literature cited above is very clear. On the other hand, a great deal of home brewer anecdotal experience seems to indicate that husk integrity can definitely affect lautering and recirculation rate, but pulverizing the husks does not necessarily cause extraction of harsh flavors. Brewers point toward other factors as causing the extraction of these compounds, which tend to be more problematic on commercial systems. Therefore the issue of undesirable flavor extraction from pulverized husks may be less worrisome for home brewers — although it's important to keep in mind this hasn't been demonstrated scientifically, and the anecdotal evidence generally doesn't discount the issues with husk pulverization possibly leading to excessive trub, haze, and decreased stability.

Oxidation

Mill with base on top of a cooler mash tun

The grist begins to oxidize immediately upon milling (because the inside of the kernels are then exposed to air) and this can have a negative impact on the subsequent beer quality. Therefore the time between milling and dough-in should be kept as short as possible.

Modern commercial low oxygen breweries fill all areas containing milled grain with inert gas (CO₂ or N₂) to prevent oxygen exposure. Brewers looking to preserve fresh grain flavor may also attempt this by flowing inert gas into the bottom of the mash tun and milling directly into it, or by flowing inert gas through the grist only after milling. Purging a mostly covered mash tun at 1–2 psi for about 10 minutes has been shown to effectively remove the vast majority of oxygen in the vessel. A regulator may start to freeze up and/or significantly chill the mash tun parts, causing dough-in temperature to be too low. A fix for that is to get a cheap heat lamp or hair dryer and point it at your regulator. Dry ice can also be used to purge: put the dry ice in a jar with water and connect it with tubing to the mash tun.

Specialty malts
Lighter color kilned or dry roasted specialty malts will crush like base malts, while caramel/crystal and extremely dark roasted products are more brittle and tend to shatter rather than crush. Malts that shatter tend to create more flour which can attribute to difficulties during lautering. The fine particles can fill in the spaces in the otherwise permeable bed causing a slowed or stuck lauter. These brittle specialty malts can typically be milled with a wider mill gap resulting in a larger particle size that will still allow for complete flavor and aroma extraction which is the primary function of these malts. Finding the balance of desired particle size starts with adjusting the mill gaps.

Wheat, rye, and oats
Generally speaking, these grains have smaller kernels and are harder than barely. Therefore the mill gap may need to be decreased when milling these grains, and more torque may be required while milling. Mill small samples to check for whole kernels, just as we suggested above for setting the gap for barley. Make a note of the ideal gap for each grain so you will know for next time.

Things that don't need to be milled

• "Flaked" or "rolled" grain adjuncts do not need to be milled, although they can be run through the mill with the rest of the grain if it is convenient.
• Rice hulls should not be put through the mill because their whole purpose is to remain intact in order to aid filtering.
• Most home brew mills are not suitable for milling corn.
• Fingers, clothing, rocks, or bits of metal should not be milled. Please be careful, especially when using power tools.

Milling location
To avoid excessive dust contaminating your gear/wort, mill away from your cold side gear and away from where you'll be chilling and fermenting your wort, particularly if you do not condition the grain.

Cleaning and maintenance

Left: dirty end plate. Right: clean end plate

First time cleaning: After adjusting the gap, mill about a pound of grain and then throw that away. This removes the machine oils from the rollers.

Cleaning after use: A paintbrush and/or compressed air will remove dust and any grain and dust clinging to the rollers.

Removing and preventing rust: Most mills have hardened steel rollers, so it is possible for them to rust. Running about a pound of grain or rice through the mill may be all that's needed to remove rust from the rollers. If that doesn't work, brush the affected area with a stainless steel brush until the rust is gone. Dust attracts moisture, so keeping the mill clean as described above will help prevent the rollers from rusting, as will storing the mill in a dry location. If you condition your grain, consider reserving a half pound of unconditioned grain to mill at the end to remove any moisture.

Maintenance: The mills we recommended above are maintenance-free, particularly if you have one with sealed ball bearings. Mills with bronze bushings may need to be disassembled and wiped clean periodically +/- lubrication. Visually check the gap setting before milling to make sure the adjustable gap is not slipping and that the rollers are in proper alignment. Rollers out of alignment may bind.

Conditioning the Grain

Simple grain conditioning setup

Dry husks fragment easily, which may cause issues (see above). However husks become more elastic when they are moist, making them easier to protect. Wetting the grain is called "conditioning". The goal is to increase the moisture content of the husk enough to minimize shredding as the grain passes through the mill. Generally the amount of water should be about 1–2% of the weight of grain. It's important not to add too much water because our mills do not like wet grain (it will stick to the rollers). The recommended amount of moisture is low enough that the grain should not be sticky and it will not cause rollers to rust. Wheat malt also benefits from conditioning.

Obviously conditioning is not a necessary step, but it does have advantages when combined with a proper roller gap and milling speed. The roller gap may need to be (and probably should be) tightened when conditioning, to make sure all the grains get crushed and to reap the benefits of more finely crushed starch. Basically all modern commercial German breweries that use lauter tuns (as opposed to mash filters) either condition their malt or mill it wet.

Advantages:

• Dust is reduced during milling.
• The risk of dough balls is decreased.
• The rollers may grip the grain better and feed faster.
• Husk volume increases (looser grain bed).
• More intact husks means that the grain can be ground more thoroughly (tighter gap) without affecting lautering.
• A tighter gap means that the starch is crushed more thoroughly.
• More thoroughly crushed starch means that efficiency and attenuation are increased and conversion is faster.
• Reduced husk damage can have quality benefits on the resulting beer. (See above)
• Manually stirring and looking at your grain allows you to find any rocks, metal pieces, or other foreign objects that may be mixed with the grain and could otherwise damage your mill.

Disadvantages:

• Additional time and labor is required.
• Milling may require additional torque.
• A roller gap adjustment is probably needed to optimize crush (and prevent uncrushed kernels).
• Protein extraction may be higher.

Method 1 (Editor's Choice)

1. Put the grain into a wide plastic tub.
2. Add water to a small spray bottle.
3. Spray the grain evenly while stirring (e.g. with your hand or a mash paddle) until the grain becomes pliable.
4. The grain may be milled about 5–10 minutes after wetting.

View this method in action:

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Method 2 (no stirring)

1. Weigh out the grain in buckets.
2. Add water to a small spray bottle.
3. Pour a thin layer into a wide plastic tub.
4. Spray it with water from a spray bottle.
5. Repeat steps 3 & 4 until done.
6. The grain may be milled about 5–10 minutes after wetting.

Method 3 (sink sprayer)

1. Put the grain into a wide plastic tub.
2. Attach a flexible misting nozzle to a sink hose.
3. Spray the grain evenly while stirring (e.g. with your hand or a mash paddle) until the grain becomes pliable.
4. The grain may be milled about 5–10 minutes after wetting.

If you are using a disc mill (like a Corona/Victoria style mill) instead of a roller mill, different amounts of moisture can possibly have variable and unpredictable effects on the resulting crush. Therefore we cannot recommend conditioning when using such a mill, but you may still experiment if you wish.

For images comparing conditioned vs unconditioned grist, see here: Grain Conditioning at LOB and Malt Conditioning at German Brewing.

Sieve Testing

We can scientifically measure the particle sizes of the crushed grain using a standardized protocol to sort the crushed grain into different size ranges using a series of sieves. This is called granulometry. Unfortunately, this process is generally not a worthwhile endeavor for home brewers due to the cost of the sieves. Nevertheless it is an excellent way to compare how different parameters can affect the crush, if you want to invest the money.

In order to test a sample that had been conditioned, it should be dried (e.g. in an oven) until the weight is stable before testing.

Here are some external resources for further reading:

• Brew Like a Pro - Malt Milling
• Beer and Wine Journal - Malt Sieves
• Brew Your Own - The Perfect Crush
• LOB forum - Ss brewtech mill review With Sieve Testing
• Book: Technology Brewing and Malting by Kunze

Examples:

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See Also

• Mills and Milling by Dave Miller (Brew Like A Pro)
• If you're really into DIY: Suggestions to help build a mill from scratch