Milling

From Brewing Forward

(In progress)

Grain (also called grist) consists mainly of starch granules 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 (endosperm) 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.[1][2]

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 container 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

A variety of options exist:

2-Roller Mills

3-Roller Mills

Motorized Mills


We have intentionally excluded the "Barley Crusher". It is a poor choice due to its soft rollers and soft/cheap bronze bushings, which lead to relatively frequent problems...[3] and then there's the sub-par customer service.[4]

Some brewers use very low budget milling options such as Corona/Victoria style mills[5] (example: Amazon), food processors, or rolling pins, but most likely you're better off buying your grain pre-milled if you're not ready to invest in a roller mill.

Reasons to buy a mill

  • Freshness - Milling immediately before brewing results in the freshest malt possible (which is especially important when using brewing techniques 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 sources 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 can buy grain in bulk.

Features to consider

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 .060" which easily pulls in both wheat and barley, softening the starch without tearing up the husk.[6] The 3-roller mill provides less husk damage, which aids in lautering (among other things). A 3-roller mill also more fully separates the starch from the husk, while providing superior grain feed. However, additional power 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[7][8] and have can a significantly longer lifespan than bushings,[9] particularly if you drive the mill with a pulley or gears.[10] Therefore we recommend a mill with bearings. However, bushings are still generally OK when using a direct drive system such as a drill. Bushings typically require periodic cleaning and lubrication with a drop of food-grade mineral oil.[11][12] A food-grade dry lubricant may possibly be used instead, although care must be taken when selecting a product.[13]

Roller diameter
Larger diameter helps the grain feed through the rollers.[1]

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.[14]

Knurled vs fluted rollers
Roller morphology is an important parameter in the resulting crush,[2] and modern commercial mills always have fluted rollers.[1] However, no home brew rollers exist that are comparable to commercial rollers. Home brew mills typically have rollers with a diamond knurling pattern, which helps feed feed grain through the gap.

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.

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. For example, less well modified malt requires finer milling.[1] The crush should be monitored every milling to ensure it is being properly crushed. Barley is an agricultural product and friability and kernel size assortment vary from maltster-to-maltster and even harvest-to-harvest.[15] It is important that you experiment with different settings and find out what works best for you. Milling ultimately is a compromise that each brewer reaches with a batch of grain.[16] The objective is to find an acceptable middle ground between efficiency (yield), lautering effectiveness, and quality.

For most systems, usually a gap in the range of 0.030" to 0.050" (0.7–1.2mm) is appropriate.[11][17] Generally it is not necessary to change the gap frequently, but crush should be monitored to ensure consistency. 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.

Un-crushed kernels with fully intact husks represent a direct loss of efficiency, so we want to avoid a so coarse (large roller gap) that it does not crush all the grain. The large difference (relatively speaking) in brewhouse efficiency is between coarse and normal crushed malt. In a normal sample, you will find no un-crushed kernels. A fine crush gives only a small increase in efficiency (relative to a normal crush), but a large increase in lauter time and difficulty.[18]

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.[18] 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. Obviously, the coarser the crush, the more intact kernels there will be, and the easier it is to find one. However, as you tighten the mill down uncrushed grains become harder to find — or to be sure they are not to be found.

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.[2] However your "mileage may vary" depending on your system, process, and ingredients.[19]

Measuring the gap
A feeler gauge should be used to adjust the gap setting. 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.[20]

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.[6][21]
  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).

Driving the Mill

Generally three options exist for powering the mill:

  1. Hand crank
  2. Drill
  3. Dedicated motor

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

Using a drill
coming soon

Using a motor
See Motorizing a mill.

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.[22][23] 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, at least in ranges that have been tested.[24]

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.[11][23] Other online sources generally suggest higher rates... around 150–300 RPM, but they also acknowledge that slower is generally better, whatever the lowest speed it can run without your drill or motor stalling.[6][14] 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.[1] This increases the effectiveness of the crush, decreasing particle size and increasing yield.[2] No home brew mills are sophisticated enough to enable this without modification. However, the benefit from speed differential is likely not worth the effort needed to modify a mill to operate in such a way, and home brew rollers are very different and so a speed differential may produce undesirable results.

Milling Considerations

There are many complexities to keep in mind.

Husk integrity
Pulverizing the whole malt into flour should be avoided.[25][24] 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.[25][26][27][28][29] 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.[1][30][31][25] 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.[32]

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).

Preventing oxidation
Oxidation processes start immediately after milling and can have a negative impact on the subsequent beer quality.[1] 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.[1] 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.[33][34] Purging a mostly covered mash tun at 1–2 psi for about 10 minutes had been shown to effectively remove the vast majority of oxygen in the vessel.[35] 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 hair dryer and set it up to blow on your regulator.[34] 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.

Sieve testing
We have ability to objectively and scientifically measure the resulting crush (called granulometry) using standardized sieves and a protocol which sort the crushed grain into different size ranges. While interesting, this is generally not a worthwhile endeavor for home brewers. However it is an excellent way to compare how different parameters can affect the crush.

Here are some external resources for further reading:


Examples:[36]

Cleaning a mill
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 clinging to the rollers.

Removing rust from rollers... Stainless steel brush? BKF? Passivate stainless steel rollers?

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.

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.[36]
  • 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.

Conditioning the Grain

Dry husks fragment easily, which may cause issues (see above).[25] However husks become more elastic when they are moist, making them easier to protect.[1][37][11][22][38] 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.[29][1][25] It's important not to add too much water because our mills do not like wet grain. The recommended amount of water is low enough that it will not cause rollers to rust. Wheat malt also benefits from conditioning.[39]

Obviously conditioning is not a necessary step, but it does have advantages when combined with a proper roller gap and milling speed.[25] 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.[40] Basically all modern commercial breweries that use lauter tuns (as opposed to mash filters) either condition their malt or mill it wet.[39]

Advantages:

  • Dust is reduced during milling.[22]
  • The risk of dough balls is decreased.[22]
  • The rollers may grip the grain better and feed faster.[22]
  • Husk volume increases (looser grain bed).[1][25]
  • More intact husks means that the grain can be ground more thoroughly (tighter gap) without affecting lautering.[1][25]
  • 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.[1][29]
  • 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 may be needed.
  • Protein extraction may be higher.[25]


Method 1 (Editor's Choice)[22]

  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:

Load video
YouTube

Method 2 (no stirring)[11]

  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)[11]

  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.[32] 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.

See Also


Potential Sources

...down the rabbit hole

References

  1. ↑ a b c d e f g h i j k l m Kunze, Wolfgang. "3.1 Milling the Malt." Technology Brewing & Malting. Edited by Olaf Hendel, 6th English Edition ed., VBL Berlin, 2019. pp. 203-218.
  2. ↑ a b c d Mousia, Z., et al. "The effect of milling parameters on starch hydrolysis of milled malt in the brewing process." Process Biochemistry, Vol. 39, No. 12, 2004, pp. 2213-2219.
  3. ↑ "Grain mill stopped working." HomeBrewTalk.com forum thread, 2018.
  4. ↑ "Barley Crusher - Customer Service????" HomeBrewTalk.com forum thread, 2012.
  5. ↑ "My Ugly Junk- Corona Mill Station..." HomeBrewTalk.com forum thread, 2008.
  6. ↑ a b c "FAQs" Monster Brewing Hardware. Accessed May 2020.
  7. ↑ "Grain Mill Recomendations." HomeBrewTalk.com forum thread, 2019.
  8. ↑ "Quality corona/hand-crank mill?" HomeBrewTalk.com forum thread, 2018.
  9. ↑ "Tell me about grain mills...." HomeBrewTalk.com forum thread, 2019.
  10. ↑ "Grain Mill Recomendation." HomeBrewTalk.com forum thread, 2019.
  11. ↑ a b c d e f "Choosing a malt mill." Low Oxygen Brewing forum thread, 2018.
  12. ↑ "Monster mill problems." HomeBrewTalk.com forum thread, 2009.
  13. ↑ "Grain mill issues." HomeBrewTalk.com forum thread, 2017.
  14. ↑ a b Green, T. "The Best Grain Mills For Homebrewing." Bison Brew. 2020.
  15. ↑ Delucchi, V. "The Perfect Crush." Brew Your Own, 2019.
  16. ↑ Hansen, B. "Practical Milling for the Craft Brewer." Briess Malt & Ingredients Co., 2007.
  17. ↑ "Dry crush mill gap." Low Oxygen Brewing forum thread, 2018.
  18. ↑ a b Miller, D. "Mills and Milling." Brew Like A Pro, 2012.
  19. ↑ "Mashing for high gelatinisation temps." Low Oxygen Brewing forum thread, 2020.
  20. ↑ "ISO/IEC 7810." Wikipedia, accessed May 2020.
  21. ↑ Ream, J. "How To: Adjust the Mill Gap of a Barley Crusher." Homebrew Engineer blog, 2015.
  22. ↑ a b c d e f "Revisiting grain conditioning." Low Oxygen Brewing forum thread, 2018.
  23. ↑ a b "Conditioned Grain Mill Gap." Low Oxygen Brewing forum thread, 2017.
  24. ↑ a b Warpala, IWS, and Pandiella, SS. "Grist Fractionation and Starch Modification During the Milling of Malt." Food and Bioproducts Processing, Vol. 78, No. 2, 2000, pp. 85-89.
  25. ↑ a b c d e f g h i Szwajgier, D. "Dry and Wet Milling of Malt. A Preliminary Study Comparing Fermentable Sugar, Total Protein, Total Phenolics and the Ferulic Acid Content in Non-Hopped Worts." J. Inst. Brew. vol. 117, no. 4, 2011, pp. 569–577.
  26. ↑ "Homebrew Grain Mills and a Pictorial Guide to Milling Grain." Winning-Homebrew.com, Accessed May 2020.
  27. ↑ Whitting, C. "Milling Your Grain." Beer & Brewer, 2018.
  28. ↑ Brown, R. "Homemade Grain Milling Systems." MoreBeer, Accessed May 2020.
  29. ↑ a b c Narziss, L., et al. Abriss der Bierbrauerei (Demolition of the brewery), 8th ed., WILEY ‐ VCH Verlag GmbH & Co. KGaA, 2017, pp. 126-130.
  30. ↑ Zepf, M. "Milling" Craft Beer & Brewing, Accessed May 2020.
  31. ↑ Siebert, K. "Haze formation in beverages." LWT, vol. 39, 2006, pp. 987–994.
  32. ↑ a b Pereira de Moura, F., and Rocha dos Santos Mathias, T. "A Comparative Study of Dry and Wet Milling of Barley Malt and Its Influence on Granulometry and Wort Composition." Beverages, vol. 4, no. 51, 2018.
  33. ↑ "CO2 purge of mash tun prior to underletting?" Low Oxygen Brewing forum thread, 2018.
  34. ↑ a b "milling into mash tun" Low Oxygen Brewing forum thread, 2019.
  35. ↑ "Purging grist in the tun." Low Oxygen Brewing forum thread, 2018.
  36. ↑ a b "Brewers Barley Flakes." Product Information Sheet, Briess, 2019.
  37. ↑ Rabe, B. Grain Conditioning Low Oxygen Brewing blog, 2016.
  38. ↑ Venturini Filho, WG. and Nojimoto, T. "Utilization of the wet milling malt steep water as raw material on brewing." Ciênc. Tecnol. Aliment. vol. 19, no. 2, 1999, pp. 174-178.
  39. ↑ a b Troester, K. Malt Conditioning. German brewing and more wiki, 2009.
  40. ↑ "Seriously bad mash efficiency suddenly!" Low Oxygen Brewing forum thread, 2019.
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