Milling: Difference between revisions

[[Category:Beer production]]

[[Grain]] consists mainly of [[starch]] granules (endosperm) inside a husk. Before the [[mashing|mash]], grain must be mechanically crushed using a mill. The crushing process breaks open the husks, exposing the starch, and also cracks the starch into smaller bits, increasing the surface area exposed to water and [[enzymes]] during mashing. We refer to this crushed grain as "grist". In general, the crush quality affects the [[mashing|mashing process]] and [[saccharification]] time, [[lautering]], [[efficiency]], [[yeast|fermentation]], and the color, taste, and overall character of the beer.<ref name="Kunze">Kunze W. Wort production. In: Hendel O, ed. [[Library|''Technology Brewing & Malting.'']] 6th ed. VBL Berlin; 2019:203–218.</ref><ref name="Mousia">Mousia Z, Balkin RC, Pandiella SS, Webb C. [https://www.sciencedirect.com/science/article/pii/S0032959203004400 The effect of milling parameters on starch hydrolysis of milled malt in the brewing process.] ''Process Biochem.'' 2004;39(12):2213–2219.</ref>

* '''Consistency''' - When the shop mills your grain, the crush size may be inconsistent.

* '''Grain conditioning''' - Milling at home gives you the option to condition your grain (see below).

===Best mills available===

|[[File:Star-6-16.png|right]]Cereal Killer, <br/>Kegco 2, <br/>Hullwrecker, <br/>Malt Muncher 2 <br/>(All the same)

|[[File:Star-6-16.png|right]]Kegco 3, <br/>Malt Muncher 3 <br/>(same)

[[File:Star-6-16.png]] = Editor's Pick

 

===Mills to avoid===

*'''The Barley Crusher''' - It has soft rollers and soft/cheap bronze bushings, which lead to relatively frequent problems and a short product lifespan.<ref>[https://www.homebrewtalk.com/threads/grain-mill-stopped-working.654248/ Grain mill stopped working.] HomebrewTalk website. 2018. Accessed 2020.</ref> Their customer service is also very poor.<ref>[https://www.homebrewtalk.com/threads/barley-crusher-customer-service.297352/ Barley Crusher - customer service????] HomebrewTalk sebsite. 2012–2018. Accessed 2020.</ref>

*'''Suspicious budget mills''' such as the [https://www.vevor.com/products/electric-grain-mill-barley-grinder-malt-crusher-hold-up-to-11lbs-crushing-dy-368 motorized] and [https://www.vevor.com/products/grain-mill-barley-grinder-malt-crusher-3-roller-wheat-home-brew-food-industry 3-roller] mills at Vevor - These cheap mills have a number of {{amazon|B07D1Y51WT|bad reviews}} and generally don't have a strong track record, so we don't recommend these products at this time.<ref>[https://www.homebrewtalk.com/threads/anyone-try-those-cheap-ebay-motorized-grain-mills.688262/ Anyone try those cheap eBay motorized grain mills?] HomebrewTalk website. 2020–2021. Accessed Jan 4 2021.</ref>

*'''Non-roller mills''' such as food processors, rolling pins, or Corona/Victoria style disc mills ({{Amazon|B00JZZKLHI|example}})<ref>[https://www.homebrewtalk.com/threads/my-ugly-junk-corona-mill-station.90849/ My ugly junk- Corona mill station.] HomebrewTalk website. 2008–2020. Accessed 2020.</ref> - These tools are not designed to create a proper crush, they're not easily adjustable, they tend to create a mess and/or require significant modification just to be useable.<ref name=bsp/> Corona-style mills are generally low-quality products (e.g. they may add metal shavings to the grist). Buy pre-milled grain until you're ready to invest in a roller mill.

=== Features ===

*'''3-roller vs 2-roller''' - In a 3-roller mill, the grain is pre-crushed in the gap between the top two rollers, and then the grain flows into the gap between the drive roller and bottom roller, crushing it further. The top gap is fixed at around 0.060–0.070" which easily pulls in both wheat and barley, providing superior feed, and softening the starch without tearing up the husk.<ref name="monster">[https://www.monsterbrewinghardware.com/store/pc/FAQs-d2.htm FAQs.] Monster Brewing Hardware. Accessed May 2020.</ref> The lowered husk damage aids in lautering among other things (see below). The double crush also more fully separates the husk from the starch. The downsides to 3-roller mills are that more power (torque) is typically required to drive them and they are generally more expensive. 2-roller mills are more budget friendly.

*'''Bearings vs bushings''' - 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.<ref>[https://www.homebrewtalk.com/threads/grain-mill-recomendations.662727/post-8529641 Grain mill recomendations.] HomebrewTalk website. 2019. Accessed 2020.</ref><ref>[https://www.homebrewtalk.com/threads/quality-corona-hand-crank-mill.645349/post-8224674 Quality corona/hand-crank mill?] HomebrewTalk website. 2018. Accessed 2020.</ref><ref>[https://www.homebrewtalk.com/threads/tell-me-about-grain-mills.666252/post-8598698 Tell me about grain mills.] HomebrewTalk website. 2019. Accessed 2020.</ref><ref>[https://www.homebrewtalk.com/threads/grain-mill-recomendation.672926/post-8734778 Grain mill recomendation.] HomebrewTalk website. 2019. Accessed 2020.</ref> On the other hand, bushings have more friction and may wear over time, such that they will need to be replaced at some point.<ref>Layosa C. [https://blog.misumiusa.com/introduction-to-working-with-linear-bushings-bushings-vs-bearings/ Introduction to working with linear bushings: bushings vs. bearings.] Misumi website. 2016. Accessed 2020.</ref><ref>[https://youtu.be/fJVGlvZQvGk Ball Bearings vs Bushings.] ServoCity on YouTube. 2017. Accessed 2020.</ref> 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.<ref name="LOB-1069">[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=18&t=1069 Choosing a malt mill.] The Modern Brewhouse website. 2018–2020. Accessed 2020.</ref><ref>[https://www.homebrewtalk.com/threads/monster-mill-problems.102809/post-1141303 Monster mill problems.] HomebrewTalk website. 2009. Accessed 2020.</ref>

*'''Roller material''' - For most brewers, hardened steel is the best option for roller material due to its durability.<ref>[https://www.reliance-foundry.com/blog/carbon-steel-versus-stainless-steel Carbon steel vs stainless steel.] Reliance Foundry. Accessed June 2020.</ref> 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.<ref name="bison">Green T. [https://bisonbrew.com/grain-mill/ The best grain mills for homebrewing.] Bison Brew. 2020. Accessed 2020.</ref><ref>[https://www.monsterbrewinghardware.com/store/pc/3-Roller-Homebrew-Grain-Mill-p86.htm 3 roller homebrew grain mill.] Monster Brewing Hardware. Accessed June 2020.</ref>

*'''Roller diameter''' - Larger diameter helps the grain feed through the rollers.<ref name="Kunze"/><ref name=mashing>Evans E. [[Library|''Mashing.'']]  American Society of Brewing Chemists and Master Brewers Association of the Americas; 2021.</ref>

*'''Knurled vs fluted rollers''' - Roller morphology has an important effect on the crush by reducing damage to the husk. Modern ''commercial'' mills always have fluted rollers.<ref name=Mousia/><ref name=Kunze/><ref name=hob11>Miedl-Appelbee M. Brewhouse technology. In: Stewart GG, Russell I, Anstruther A, eds. [[Library|''Handbook of Brewing.'']] 3rd ed. CRC Press; 2017.</ref> On the other hand, most home brew mills have rollers with a diamond knurling pattern, which is necessary to improve the grain feed through small diameter rollers. A few home brew mills with relatively larger rollers (e.g. MattMill and Ss Brewtech) have a fluted morphology. However, the fluting pattern on these is completely different than commercial mills,<ref name=Kunze/> so it is unclear whether the fluting provides any benefit over knurling for home milling.

*'''Drive shaft''' - A 1/2" integrated drive shaft is the most durable. If you have a drill that you plan to use for milling, verify that it can fit on the drive shaft for the mill you want to purchase.

*'''Hopper size''' - Hopper size is a matter of convenience and budget. It is most convenient to add the grain to the hopper all at once, however it doesn't hurt anything if you need to pause partway through milling in order to fill the hopper with more grain. Portability, weight, and storage space should be also be taken into account. Some mills have optional hopper extensions to purchase, or you can make a hopper extension yourself.

*'''Throughput rate''' - Differences in roller length and how fast the rollers feed grain is generally negligible for home brewers and not something that needs to be considered. Throughput depends largely on drive speed (RPM) and not the particular mill characteristics.

*'''Roller speed differential''' - Modern large-scale commercial mills have the rollers spinning at different speeds.<ref name=Kunze/> This increases the effectiveness of the crush by shearing off the husk from the endosperm, which serves to increase yield while reducing husk damage.<ref name=Mousia/> The only home brew mill with speed differential is from Ss Brewtech.

FYI, any Monster Mill accessories like {{Amazon|B0064OMA04|this base}} will also work for the Kegco 3-roller mill.

For most home brewers a drill is the preferred method to drive a mill. It is 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 torque. We don't recommend using an external speed limiter ({{Amazon|B00U3LD1WA|example}}) on a high RPM drill because they significantly reduce the torque.<ref>[https://www.homebrewtalk.com/threads/speed-controller-for-corded-drill-used-for-milling-grain.629645/ Speed controller for corded drill, used for milling grain?] HomebrewTalk website. 2017. Accessed 2020.</ref><ref>[https://www.homebrewersassociation.org/forum/index.php?topic=23703 Monster mill drill question.] American Homebrewers Association website. 2015. Accessed 2020.</ref> Affixing a zip tie, 2" tri-clamp, or U-bolt 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.<ref>[https://www.beeradvocate.com/community/threads/need-drill-recommendations.581479/ Need drill recommendations.] BeerAdvocate website. 2018. Accessed 2020.</ref><ref>[https://www.homebrewersassociation.org/forum/index.php?topic=9367 Proper drill for milling grain.] American Homebrewers Association website. 2011. Accessed 2020.</ref> 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]). 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.

All of the mills we recommend have an adjustable roller gap. A tighter gap produces smaller grain particles, called a fine crush, and a larger gap creates a coarse crush. '''There is not a one-size-fits-all gap setting.''' The ideal mill gap setting is dependent on your mill, your brewing system, and factors related to the grain (which can vary even from batch to batch and with storage time).<ref name=Kunze/><ref name=Crescenzi>Crescenzi AM. [https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2050-0416.1987.tb04498.x Factors governing the milling of malt.] ''J Inst Brew.'' 1987;93:193–201.</ref><ref name=delucchi>Delucchi V. [https://byo.com/article/the-perfect-crush/ The perfect crush.] Brew Your Own website. 2019. Accessed January 2021.</ref> For each batch the objective is to find an acceptable middle ground between lautering/recirculation effectiveness, efficiency (yield), and quality.<ref name="Briess">Hansen B. [http://www.brewingwithbriess.com/Assets/Presentations/Briess_2007CBC_Practical_Milling.ppt Practical milling for the craft brewer.] Briess Malt & Ingredients Co. 2007. Accessed 2020.</ref><ref name=smart3>Holbrook CJ. Brewhouse operations. In: Smart C, ed. [[Library|''The Craft Brewing Handbook.'']] Woodhead Publishing; 2019.</ref> Some experimentation with different settings is needed to find out what works best for your mill and your brewing system, although there is a wide range that will be adequate.<ref>[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=2&t=1795 Mashing for high gelatinisation temps.] The Modern Brewhouse website. 2020. Accessed 2020.</ref> Also, the grist should be visually monitored every milling to ensure it is being properly crushed.

[https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2005.tb00690.x Effects of mashing parameters on mash β-glucan, FAN and soluble extract levels.] ''J Inst Brew.'' 2005;111(3):316–327.</ref> This greatly depends on your system/process, and experimentation is required to find the smallest acceptable gap. For example, a simple BIAB system can tolerate a fine crush, whereas a recirculating system tends to benefit from more intact husks. Keep in mind that excessive husk damage can potentially affect beer quality (see below).<ref name=Mousia/> Also be aware that 2-roller mills have a lower limit at which the rollers can feed the grain.

# On mills with adjustment knobs, mark on the frame what the gap is at the a variety of knob positions. This way you can repeat different gap settings without getting out your feeler gauge again. We suggest marking increments every 0.005" (0.1mm) over a range of 0.020" to 0.055" (0.5–1.4mm).

Several things should be considered when deciding on mill gap and other parameters that will affect grist performance during mashing.

Pulverizing the entire grain into flour should generally be avoided.<ref name="Szwajgier">Szwajgier D. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2011.tb00505.x 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.'' 2011;117(4):569–577.</ref><ref name=Warpala>Warpala IWS, Pandiella SS. [https://www.sciencedirect.com/science/article/abs/pii/S0960308500701982 Grist fractionation and starch modification during the milling of malt.] ''Food and Bioproducts Processing.'' 2000;78(2):85–89.</ref> A high percentage of flour will increase the viscosity of the wort, increasing the likelihood of the dreaded "stuck mash" or slow recirculating and lautering. 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.<ref name="Szwajgier"/><ref>[https://www.winning-homebrew.com/homebrew-grain-mills.html Homebrew grain mills and a pictorial guide to milling grain.] Winning-Homebrew.com website. Accessed May 2020.</ref><ref name=brewer>Whitting C. [https://www.beerandbrewer.com/milling-your-grain/ "Milling Your Grain."] Beer & Brewer. 2018. Accessed 2020.</ref><ref name=more>Brown R. [https://www.morebeer.com/articles/DIY_Homebrew_Grain_Mill Homemade grain milling systems.] MoreBeer. Accessed May 2020.</ref><ref name=adb>Narziss L, Back W, Gastl M, Zarnkow M. [[Library|''Abriss der Bierbrauerei.'']] 8th ed. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA; 2017:126–130.</ref><ref name=fix>Fix G. [[Library|''Principles of Brewing Science.'']] 2nd ed. Brewers Publications; 1999.</ref> Excessive milling promotes the extraction and solubilization of undesirable compounds into the wort and beer, such as [[silicates]], [[fatty acids|lipids]], husk-derived tannins ([[phenolic compounds]]), and large-molecular [[protein]]s, which can cause excess formation of [[trub]], deposits, color changes, [[haze]]s, and a shorter shelf life.<ref name=Kunze/><ref>Zepf M. [https://beerandbrewing.com/dictionary/VWpGLEPUS6/ Milling.] Craft Beer & Brewing. Accessed May 2020.</ref><ref>Siebert KJ. [https://www.sciencedirect.com/science/article/pii/S0023643806000259 Haze formation in beverages.] ''Lebenson Wiss Technol.'' 2006;39(9);987–994.</ref><ref name=Szwajgier/><ref name=Moura>Pereira de Moura F, Rocha dos Santos Mathias T. [https://www.mdpi.com/2306-5710/4/3/51/pdf A comparative study of dry and wet milling of barley malt and its influence on granulometry and wort composition.] ''Beverages.'' 2018;4(51).</ref><ref name=golston/><ref name=pre>Prechtl C. [https://www.mbaa.com/publications/tq/tqPastIssues/1967/Abstracts/tq67ab16.htm Some practical observations concerning grain bitterness in beers and its amelioration.] ''Tech Q Master Brew Assoc Am.'' 1967;4(1):98–103.</ref> Lastly, too much husk flour can potentially result in loss of [[extract]] because starch will be adsorbed to the husk and discarded with it.<ref name=esslinger>Krottenthaler M, Back W, Zarnkow M. Wort production. In: Esslinger HM, ed. [[Library|''Handbook of Brewing: Processes, Technology, Markets.'']] Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA; 2009.</ref>

Husk integrity can be improved by conditioning the grain, by using an appropriately large mill gap, and by using a 3-roller mill or a mill with fluted rollers.

In general, a milling speed between 50–300 RPM is considered appropriate.<ref name="lob271"/><ref name="LOB-1069"/><ref name="monster"/><ref name="bison"/> Be aware that it usually takes a little more torque to get the mill going. If your drive method is struggling, use the method to reduce torque described above.

Some home brewers have found that milling at a lower speed reduces damage to husks.<ref name=lob993/><ref name=lob271>[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=2&t=271 Conditioned grain mill gap.] The Modern Brewhouse website. 2017–2018. Accessed 2020.</ref><ref>[https://www.homebrewtalk.com/threads/so-what%E2%80%99s-the-right-harbor-freight-drill-for-a-mill-20-off-coupon-out-now.673941/ So what's the right Harbor Freight drill for a mill? 20% off coupon out now.] HomebrewTalk website. 2020. Accessed 2020.</ref> Other brewers have not noticed a significant effect of milling speed on the grist (appearance or granulometry),<ref>[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=11&t=1929 Milling test results.] The Modern Brewhouse website. 2020. Accessed July 2020.</ref><ref name=bittner/> which is in agreement with professional literature.<ref name=Warpala/><ref name=Mousia/>

The grist begins to [[Oxidation|oxidize]] immediately upon milling (because the inside of the kernels are then exposed to air and moisture) and this can have a negative impact on the subsequent beer quality.<ref name=Kunze/><ref name=adb/><ref name=pasame>Pascoe HM, Ames JM, Chandra S. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-61-0203 Critical stages of the brewing process for changes in antioxidant activity and levels of phenolic compounds in ale.] ''J Am Soc Brew Chem.'' 2003;61(4):203–209.</ref> Therefore the time between milling and dough-in should be kept as short as possible.<ref name=golston>Golston AM. [https://www.mbaa.com/publications/tq/tqPastIssues/2021/Pages/TQ-58-1-0322-01.aspx The impact of barley lipids on the brewing process and final beer quality: A mini-review.] ''Tech Q Master Brew Assoc Am.'' 2021;58(1):43–51.</ref>

Modern commercial low oxygen breweries fill all areas containing milled grain with inert gas (CO₂ or N₂) to prevent oxygen exposure.<ref name=Kunze/><ref name=bsp/><ref name=adb/><ref name=derouck/><ref name=golston/> Brewers looking to [[low oxygen brewing|preserve fresh grain flavor]] may do this simply by flowing inert gas into the bottom of the mash tun and milling directly into it, or by flushing the grist with inert gas after milling.<ref name=stephenson>Stephenson WH, Biawa JP, Miracle RE, Bamforth CW. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2003.tb00168.x Laboratory-scale studies of the impact of oxygen on mashing.] ''J Inst Brew.'' 2003;109(3):273–283.</ref><ref name=mullerr>Muller R. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-53-0053 Use of 5,5’-dithiobis (2-nitrobenzoic acid) as a measure of oxidation during mashing.] ''J Am Soc Brew Chem.'' 1995;53(2):53–58.</ref><ref>[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=2&t=1025 CO2 purge of mash tun prior to underletting?] The Modern Brewhouse website. 2018. Accessed 2020.</ref><ref name="lob1394">[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=18&t=1394 Milling into mash tun.] The Modern Brewhouse website. 2019. Accessed 2020.</ref> 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.<ref>[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=11&t=751 Purging grist in the tun.] The Modern Brewhouse website. 2018. Accessed 2020.</ref> 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.<ref name="lob1394"/> 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. Note that flushing with inert gas during the actual milling process appears not to be entirely critical, as oxidation does not occur immediately (at least with regard to [[lipids]]).<ref name=wackerbauer>Wackerbauer K, Meyna S, Marre S. [http://themodernbrewhouse.com/wp-content/uploads/2017/04/174-178.pdf Hydroxy fatty acids as indicators for ageing and the influence of oxygen in the brewhouse on the flavour stability of beer.] ''Monatsschrift Brauwiss.'' 2003;56(9/10):174–178.</ref>

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.<ref>Geurts J. [http://blog.brewingwithbriess.com/9-5-grind/ 9-5 grind.] Briess blog. 2018. Accessed 2020.</ref>

To avoid excessive dust contaminating your gear and wort, it's considered prudent to 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. Conditioning can help lower the amount of dust generated while milling. However, dust can still be created when measuring the grain. Wearing a mask can be beneficial for your health since breathing in grain dust is not so great. Thanks to COVID-19 you do have a mask, right?

Sieves can be used to scientifically measure the particle sizes of the grist. This is called granulometry, or sieve testing. Unfortunately, the sieves are a bit expensive and the testing process is somewhat labor-intensive. Furthermore, the results are borderline useless since the crush produced by home brew mills differs greatly from that of a commercial mill, even with similar granulometry results.<ref name=bittner>Bittner A. [https://brewingforward.com/sieve-testing/ Think like a scientist: Sieve testing.] Brewing Forward website. 2021. Accessed February 2021.</ref> Therefore, we do not recommend home brewers invest in the materials or effort required for sieve testing.