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# 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).
# 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).


==Milling considerations==
== Milling considerations ==
There are many complexities to keep in mind.
Several things should be considered when deciding on mill gap and other parameters that will affect grist performance during mashing.


===Husk integrity===
=== Husk integrity ===
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, 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>
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>


However, fine milling does not ''necessarily'' cause extraction of harsh flavors, and it can be acceptable depending on the [[lautering]] method.<ref name=bsp>Briggs DE, Boulton CA, Brookes PA, Stevens R. [[Library|''Brewing Science and Practice.'']] Woodhead Publishing Limited and CRC Press LLC; 2004.</ref><ref name=derouck>De Rouck G, Jaskula-Goiris B, De Causmaecker B, et al. [https://www.brewingscience.de/index.php?tpl=table_of_contents&year=2013&edition=0001%252F0002&article=82374 The impact of wort production on the flavour quality and stability of pale lager beer.] ''BrewingScience.'' 2013;66(1/2):1–11.</ref> [[brewing pH|Mash pH]] strongly influences the extraction of negative compounds, which can be particularly troublesome when [[Sparging|fly sparging]]. Therefore the issue of undesirable flavor extraction from pulverized husks may be less worrisome for home brewers who properly control mash and sparge pH, although husk pulverization may still lead to other issues such as haze and excessive trub depending on other factors.<ref>De Rouck G, Jaskula B, De Causmaecker B, et al. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2013-0113-01 The influence of very thick and fast mashing conditions on wort composition.] ''J Am Soc Brew Chem.'' 2013;71(1):1–14.</ref>
However, fine milling does not ''necessarily'' cause extraction of harsh flavors, and it can be acceptable depending on the [[lautering]] method.<ref name=bsp>Briggs DE, Boulton CA, Brookes PA, Stevens R. [[Library|''Brewing Science and Practice.'']] Woodhead Publishing Limited and CRC Press LLC; 2004.</ref><ref name=derouck>De Rouck G, Jaskula-Goiris B, De Causmaecker B, et al. [https://www.brewingscience.de/index.php?tpl=table_of_contents&year=2013&edition=0001%252F0002&article=82374 The impact of wort production on the flavour quality and stability of pale lager beer.] ''BrewingScience.'' 2013;66(1/2):1–11.</ref> [[brewing pH|Mash pH]] strongly influences the extraction of negative compounds, which can be particularly troublesome when [[Sparging|fly sparging]]. Therefore the issue of undesirable flavor extraction from pulverized husks may be less worrisome for home brewers who properly control mash and sparge pH, although husk pulverization may still lead to other issues such as haze and excessive trub depending on other factors.<ref>De Rouck G, Jaskula B, De Causmaecker B, et al. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2013-0113-01 The influence of very thick and fast mashing conditions on wort composition.] ''J Am Soc Brew Chem.'' 2013;71(1):1–14.</ref>
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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/>
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/>


===Oxidation===
=== Oxidation ===
[[File:Mill-on-cooler.jpg|thumb|right|Mill with base on top of a cooler mash tun]]
[[File:Mill-on-cooler.jpg|thumb|right|Mill with base on top of a cooler mash tun]]
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>
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>
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Modern commercial low oxygen breweries fill all areas containing milled grain with inert gas (CO<sub>2</sub> or N<sub>2</sub>) 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>
Modern commercial low oxygen breweries fill all areas containing milled grain with inert gas (CO<sub>2</sub> or N<sub>2</sub>) 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>


===Grain moisture===
=== Grain moisture ===
The moisture content of the malt influences the fineness of the grist. Moisture makes the grain more elastic and the crush becomes more coarse. Coarse particles adhering to the husks are more difficult to degrade during the mashing process, leading to a lower yield. This mainly applies to malts which, if improperly stored, have a water content of 8–12%. Unlike with grain conditioning, this moisture is distributed through the entire grain. On the other hand, a malt with very little moisture has a tendency to be crushed too fine, destroying the husks and increasing the flour content. This may occur when very young dark malts are used, which is probably an unlikely situation for home brewers. Conditioning may help avoid problems in both of these cases, although minimizing moisture during [[grain]] storage is still a high priority.<ref name=adb/>
The moisture content of the malt influences the fineness of the grist. Moisture makes the grain more elastic and the crush becomes more coarse. Coarse particles adhering to the husks are more difficult to degrade during the mashing process, leading to a lower yield. This mainly applies to malts which, if improperly stored, have a water content of 8–12%. Unlike with grain conditioning, this moisture is distributed through the entire grain. On the other hand, a malt with very little moisture has a tendency to be crushed too fine, destroying the husks and increasing the flour content. This may occur when very young dark malts are used, which is probably an unlikely situation for home brewers. Conditioning may help avoid problems in both of these cases, although minimizing moisture during [[grain]] storage is still a high priority.<ref name=adb/>


===Specialty grains===
=== Specialty grains ===
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>
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>


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* Fingers, clothing, rocks, or bits of metal should not be milled. Please be careful, especially when using power tools.
* Fingers, clothing, rocks, or bits of metal should not be milled. Please be careful, especially when using power tools.


===Dust===
=== Dust ===
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?
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?


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