Editing Mashing

Mashing is the most important process in [[brewing|wort production]]. During this step, the [[milling|milled]] grain is mixed with hot [[water]]. Natural malt [[enzymes]] break down the [[starch]] and other grain components, creating a fermentable [[wort]]. All of the substances that go into solution are referred to as [[extract]], which include [[sugars]], minerals, and [[protein]]s. The mashing process offers various possibilities for the brewer to influence the character of the final [[beer]].<ref name=kunze>Kunze W. Hendel O, ed. [[Library|''Technology Brewing & Malting.'']] 6th ed. VLB Berlin; 2019.</ref><ref name=smart3>Holbrook CJ. Brewhouse operations. In: Smart C, ed. [[Library|''The Craft Brewing Handbook.'']] Woodhead Publishing; 2019.</ref>

Starting with mash-in and continuing throughout the entire brewing process, it is important to control both the temperature and the [[brewing pH|pH]] of the wort.<ref name=kunze/> Mash duration is normally 1–2 hours. A longer mash should be avoided because [[oxidation]] and excessive [[protein|protein degradation]] can decrease the beer quality.<ref name=kunze/><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.</ref> During this time, the mash may be held at one temperature (single infusion mashing) or more than one temperature (step mashing). It is beneficial to conduct mashing operations as oxygen-free as possible.<ref name=kunze/><ref name=bsp/><ref name=adb/><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=sacher/><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><ref>Kunz T, Brandt NO, Seewald T, Methner FJ. [https://www.researchgate.net/publication/281405909_Carbohydrates_Addition_during_Brewing_-_Effects_on_Oxidative_Processes_and_Formation_of_Specific_Ageing_Compounds Carbohydrates addition during brewing – effects on oxidative processes and formation of specific ageing compounds.] ''BrewingScience.'' 2015;68(7):78–92.</ref><ref name=golston>Golston AM. 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><ref name=arts>Arts MJTJ, Grun C, De Jong RL, et al. [http://themodernbrewhouse.com/wp-content/uploads/2017/01/Oxidative-degradation-of-lipids-during-mashing..pdf Oxidative degradation of lipids during mashing.] ''J Agric Food Chem.'' 2007;55(17):7010–7014.</ref><ref name=kanbam/><ref name=bammul>Bamforth CW, Muller RE, Walker MD. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-51-0079 Oxygen and oxygen radicals in malting and brewing: a review.] ''J Am Soc Brew Chem.'' 1993;51(3):79–88.</ref>

'''Mashing Process Overview:'''
# '''Prepare the water''': Heat, adjust mineral content, deoxygenate, etc.; see [[Water]].
# '''Mash-in''': Mix the milled grains and water together.
# '''Wait''': Allow time for the enzymes to work.
#: The following activities are optional during the mash:
#* Change the temperature (step mashing).
#* Measure the [[pH testing|pH]].
#* Monitor wort density.
#* Vorlauf or recirculate.

Mashing is followed by a [[lautering]] step where the [[wort]] is separated from the [[spent grains]]. Optionally, the spent grain can then be  [[sparging|sparged]] (rinsed with additional water) to increase [[extract]].

== Transformations During Mashing ==
Chemical and physical changes take place while mashing, transforming the starchy malt into a nutrient-rich liquid that [[yeast]] can ferment into [[beer]]. Here's an overview of what's occurring:

=== Starch degradation ===
A necessary step in the production of beer is the degradation of [[starch]] into fermentable [[Sugars and dextrins|sugars]] by [[enzymes]]. These sugars are what the [[yeast]] will convert into [[alcohol]]. Starch degradation occurs in three stages (see [[Starch]] for more detailed information):<ref name=kunze/>
# '''Gelatinization''' - The starch granules hydrate, so that they are more susceptible to enzymatic degradation.
# '''Liquefaction''' - Viscosity of the gelatinized starch is rapidly reduced by α-amylase enzymes.
# '''Saccharification''' - Enzymes α-amylase, β-amylase, and limit dextrinase degrade the starch to form glucose, maltose, maltotriose, and dextrins.

Full conversion of starch to sugars is desirable since it makes the best use of the malt and is necessary to obtain clear beer.<ref name=kunze/><ref name=mashing/>

=== Other processes ===
Besides starch degradation, there are many other processes occurring during the mash, and the impact of these changes are extremely complex. Here's a simplified overview of some important compounds being extracted:
*'''Proteins''' are extracted and partly degraded into smaller proteins, peptides, and [[amino acids]], which are important for [[yeast|fermentation]], [[foam]], [[mouthfeel]], and [[flavor stability]], but can also contribute to [[haze]]. See [[Protein]].
*'''Lipids''' are extracted and partly degraded to form glycerin and free fatty acids, which the yeast consume during fermentation. Oxidation of lipids can lead to off-flavors. See [[Lipids]].
*'''β-glucans and arabinoxylans''' are extracted. These "gums" contribute to mouthfeel, but they can cause wort flow problems when oxidized. See [[Beta-glucans and arabinoxylans]].
*'''Phenolic compounds''' are extracted. These natural [[antioxidants]] contribute to [[flavor stability]], but they can have negative effects if they become oxidized. See [[Phenolic compounds]].
*'''Phosphates''' are extracted, which are essential for [[yeast|fermentation]] and also affect the pH. See [[Phosphates]].
*'''Zinc''' is extracted, which is important for  [[yeast|fermentation]]. See [[Zinc]].

== Strike water ==
The water used for mash-in is called ''strike water''. The details of water preparation are discussed separately. See [[Water]]. Here is a summary:

Procedure:
# Use the right '''volume''' of water, based on the recipe and brewing system.
#: If sparging, the water should be evenly split between the mash and sparge.<ref name=kunze/><ref name=fix>Fix G. [[Library|''Principles of Brewing Science.'']] 2nd ed. Brewers Publications; 1999.</ref>
# Use the right '''temperature''' of water, based on the desired mash temperature and the amount of grain.<ref name=kunze/>

Best practices:
* Adjust the calcium to the ideal range.
* Adjust the flavor ions (especially chloride and sulfate) based on the recipe.
* Adjust acid/base as needed for target mash pH.
* Remove dissolved oxygen.
* [[Remove chlorine from tap water|Remove chlorine or chloramine]], if applicable.

{|Class="wikitable" style="text-align: left; float:right; margin-left: 10px;"
!Mash thickness !! L/kg !! gal/lb !! qt/lb
|-
! Thin
| 3.5 || 0.42 || 1.7
|-
! Normal
| 2.7 || 0.32 || 1.3
|-
! Thick
| 1.5 || 0.18 || 0.73
|}
Note:<br/>
A mash can be described as "thick" or "thin"; a thin mash has more water relative to the amount of grain. Mash thickness can have some influence on mashing processes, such as protein degradation and starch degradation. However, these effects are negligible unless the mash is very thick.<ref name=kunze/><ref name=fix/><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=adb/><ref name=derouckg/><ref name=kuhbeck/><ref name=iyumad/><ref name=mulcarb/> Therefore, '''small-scale brewers do not need to adjust mash thickness''' to influence the final beer.<ref name=kall>Kallmeyer M. [https://draymans.com/to-mash-or-not-to-mash-kurzhoch/ To mash or not to mash Kurz/Hoch.] Drayman's Brewery website. 2016. Accessed online March 2024.</ref><br style="clear:all;"/>

== Mashing-In ==
Mash-in, also called dough-in, is the mixing of the [[water]] and [[milling|milled]] grist. Mash-in must be performed so that the water and grist are thoroughly mixed together without any clumping. Clumps (i.e. "dough balls") may form by the agglutination of fine particles, and these are very difficult to dissolve and can ultimately lead to undegraded [[starch]] in the wort, low [[efficiency]], and/or lower [[attenuation]].<ref name=kunze/><ref name=bsp/><ref name=adb/>

'''Modern mash-in procedure:'''<br/>
The grist is placed in the mash vessel, which is then slowly filled from below with deaerated strike water; this is called ''underletting''.<ref name=kunze/><ref name=bsp/><ref name=golston/><ref name=adb/> This method greatly reduces the amount of oxygen getting into the mash, helping to avoid [[oxidation]]. Ideally you would also flush the mashing vessel with inert gas (such as CO<sub>2</sub> or N<sub>2</sub>) before adding the water.<ref name=stephenson/><ref name=mullerr/><ref name=golston/> Anecdotally, underletting also helps to avoid dough balls.<ref>[https://www.homebrewtalk.com/threads/underletting-for-mash-in.659997/ Underletting for mash-in.] Homebrew Talk website. 2018. Accessed 2020.</ref><ref>[https://www.homebrewtalk.com/threads/reverse-dough-in.537260/ Reverse dough-in.] Homebrew Talk website. 2015. Accessed 2020.</ref><ref>[https://www.homebrewersassociation.org/forum/index.php?topic=32591.0 Pumping into mashtun from HLT.] American Homebrewers Association website. 2018. Accessed 2020.</ref><ref>[https://www.homebrewtalk.com/threads/which-hot-side-low-oxygen-steps-have-you-implemented.699050/post-9242347 Which hot-side low oxygen steps have you implemented?] Homebrew Talk website. 2022. Accessed online March 2024.</ref>

'''Traditional mash-in procedure:'''<br/>
The grist is added to the strike water while stirring with a [[mash paddle]]. The major drawback to this method is that it causes a lot of oxygen to enter the mash along with the inflowing grist (increasing [[oxidation]]).<ref name=kunze/><ref name=hob11/><ref name=adb/> Also, dough balls may form if the grist is added too quickly, which then need to be broken up by stirring (further increasing oxidation).<ref name=bsp/> Adding water to grist from above will add even more oxygen. The traditional mash-in method is fine for beginners or any brewers willing to accept oxidizing the wort.

== Heat loss prevention ==
During mashing, excessive heat loss should be avoided since a big temperature drop will extend the amount of time needed to heat the wort to a [[boiling|boil]], and potentially could negatively affect [[enzymes|enzyme]] activity. However, a small drop in temperature during the mash will not cause any problems.<ref name=Vriesekoop>Vriesekoop F, Rathband A, MacKinlay J, Bryce JH. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2010.tb00425.x The evolution of dextrins during the mashing and fermentation of all-malt whisky production.] ''J Inst Brew.'' 2010;116(3):230–238.</ref> The easiest way to maintain temperature is to '''insulate the mash vessel'''. Home brewers often use blankets, towels, sleeping bags, or Reflectix-type insulation ({{amazon|B000BPF22U}}) for insulation. Always keep flammable materials away from fire. Using a beverage cooler as a mash vessel is also common among home brewers, and it insulates the mash quite well by design. Other creative options exist. For example, brewers with a small mash vessel may put it in a pre-heated oven (turned off) for the duration of the mash. The ultimate way to control mash temperature is to use a '''heated recirculating system''' (HERMS or RIMS), although it does increase risk of [[oxidation]], and it is more complicated and expensive. These types of advanced systems are probably overkill for single-infusion mashing. Commercial-scale brewers generally don't need to worry about excessive heat loss since the larger volume of wort has a larger thermal mass and less surface area for losing heat (relative to the volume).

We do NOT recommend directly heating the mash to compensate for heat loss, since it can cause problems such as scorching the wort or cause excessive and/or uneven heating (creating areas in the mash that are too hot).<ref name=adb/>

== Single-infusion mashing ==
{| class="wikitable" style="float:right; margin-left: 10px;"
|+Single-infusion mash schedule:
|-
|
<ol>
<li style="margin-left:-20px; margin-right: 10px;">149°F (65°C) for 60 minutes</li>
</ol>
|}
The simplest method is to hold the mash at one temperature that serves as a compromise between starch [[starch|gelatinization]] and the optimal temperature ranges of certain starch-degrading [[enzymes]] (β-amylase and limit dextrinase).<ref name=evans>Evans DE, Fox GP. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2017-4707-01 Comparison of diastatic power enzyme release and persistence during modified Institute of Brewing 65°C and Congress programmed mashes]. ''J Am Soc Brew Chem.'' 2017;75(4):302–311.</ref><ref name=foxsta>Fox GP, Staunton M, Agnew E, D'Arcy B. [https://onlinelibrary.wiley.com/doi/full/10.1002/jib.585 Effect of varying starch properties and mashing conditions on wort sugar profiles.] ''J Inst Brew.'' 2019;125(4):412–421.</ref> This is referred to as a "single-infusion" or "isothermal" mashing. A temperature of 144°F (62°C) is the minimum recommended for a single-infusion mash, and this will produce the most fermentable wort.<ref name=kunze/><ref name=fix/> Mashing should generally be in the range of 144–151°F (62–66°C), since it yields the maximum [[extract]] for single-infusion.<ref name=bsp/><ref name=adb/> More specifically, '''149°F (65°C) is accepted as the ideal temperature''' for a 60-minute single-infusion mash.<ref name=smart3/><ref name=hob11/><ref>Fox GP. Starch in brewing applications. In: Sjöö M, Nilsson L, eds. ''Starch in Food.'' 2nd ed. Woodhead Publishing; 2017:633–659.</ref><ref name=guerra>Guerra NP, Torrado-Agrasar A, López-Macías C, et al. Use of Amylolytic Enzymes in Brewing. In: Preedy VR, ed. ''Beer in Health and Disease Prevention.'' Academic Press; 2009:113–126.</ref><ref name=evans/><ref name=mashing>Evans E. [[Library|''Mashing.'']]  American Society of Brewing Chemists and Master Brewers Association of the Americas; 2021.</ref><ref name=assessing>Evans DE, Collins H, Eglinton J, Wihelmson A. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-63-0185 Assessing the impact of the level of diastatic power enzymes and their thermostability on the hydrolysis of starch during wort production to predict malt fermentability.] ''J Am Soc Brew Chem.'' 2005;63(4):185–198.</ref><ref>Evans DE, Li C, Eglinton JK. [https://www.researchgate.net/publication/226691242_The_Properties_and_Genetics_of_Barley_Malt_Starch_Degrading_Enzymes The properties and genetics of barley malt starch degrading enzymes.] In: Zhang G, Li C, eds. [[Library|''Genetics and Improvement of Barley Malt Quality.'']] Springer; 2010:143–189.</ref><ref name=yu>Yu W, Zhai H, Xia G, et al. [https://www.sciencedirect.com/science/article/abs/pii/S0924224420306002 Starch fine molecular structures as a significant controller of the malting, mashing, and fermentation performance during beer production.] ''Trends Food Sci Technol.'' 2020;105:296–307.</ref><ref name=mulcarb/><ref>Evans DE, Goldsmith M, Dambergs R, Nischwitz R. [https://www.researchgate.net/profile/David-Evan-Evans/publication/277808631_A_Comprehensive_Revaluation_of_Small-Scale_Congress_Mash_Protocol_Parameters_for_Determining_Extract_and_Fermentability/links/578ebce408aecbca4caad696/A-Comprehensive-Revaluation-of-Small-Scale-Congress-Mash-Protocol-Parameters-for-Determining-Extract-and-Fermentability.pdf A comprehensive revaluation of small-scale congress mash protocol parameters for determining extract and fermentability.] ''J Am Soc Brew Chem.'' 2011;69(1):13–27.</ref> Around 155°F (68°C) or higher, fermentability begins to decrease sharply and [[lipids|fatty acid]] levels may be negatively affected.<ref name=evans/><ref name=mulcarb/> The main reason to decrease wort fermentability is to brew a low-alcohol beer.<ref name=guerra/> Keep in mind that these temperatures are just guidelines — extract and fermentability also depend on the characteristics of the [[malt]].

== Step mashing ==
An advanced method of mashing is to move the mash among ''multiple'' temperatures in order to gain benefits that occur from mashing in particular temperature ranges.<ref name=kunze/> This method is called a "step mash", and the periods where the temperature is held stable are called "rests". Typically, the mash starts at the lowest temperature rest, and after some period of time it is heated in order to reach the higher rest, repeating as necessary for any other desired rests. Step mashing can produce wort with good fermentability resulting from a low temperature rest, as well as good body, [[foam]], and [[efficiency]] from a higher rest, a combination of attributes beyond that which can be achieved by a single-infusion mash.<ref name=langenaekena>Langenaeken NA, De Schepper CF, De Schutter DP, Courtin CM. [https://www.sciencedirect.com/science/article/abs/pii/S030881461930843X Different gelatinization characteristics of small and large barley starch granules impact their enzymatic hydrolysis and sugar production during mashing.] ''Food Chem.'' 2019;295:138–146.</ref> The most common mashing process in Germany is known as the ''Hoch-Kurz'' (literally "high-short").<ref name=fix/><ref name=sacher/> It eliminates the lower rests used in traditional mash schedules, and total time is around an hour. The positive effects from Hoch-Kurz mashing are evident in enhanced foam formation and stability, a more pleasant mouthfeel, less haze, lighter color, improved flavor, and improved flavor stability.<ref name=sacher>Sacher B, Becker T, Narziss L. [http://www.themodernbrewhouse.com/wp-content/uploads/2017/04/pkjdf.pdf Some reflections on mashing – Part 1.] ''Brauwelt International.'' 2016;5:309-311.</ref><ref name=derouckg/><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><ref name=adb/> One caveat is that modern (highly-modified) [[malt]] is required for this process. Other types of step mashing can sometimes be used to create specialty beers such as a [[cereal mash]], [[decoction mash]], a [[maltase mash]], or a [[turbid mash]].

=== Step mashing schedule ===
Before mashing, you need a plan for the rest temperatures and durations, i.e. a "mash schedule". Generally, all rests below 142°F (61°C), such as a "protein rest" at 113–131°F (45–55°C), should be avoided due to the increased time and energy required, worse [[foam]], and decreased [[flavor stability]].<ref name=kunze/><ref name=derouckg>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><ref name=mullerr/><ref name=cvengro>Cvengroschová M, Šepel'ová G, Šmogrovičová D. [https://www.themodernbrewhouse.com/wp-content/uploads/2017/04/128-131.pdf Effect of mashing-in temperature on free amino nitrogen concentration and foam stability of beer.] ''Monatsschrift Brauwiss.'' 2003;56(7/8):128–131.</ref><ref name=kall/> The one exception to this is for mashing poorly-modified malt, which may benefit from such a rest to help degrade [[protein]] and [[beta-glucans|β-glucans]] (see [[Malt]]).<ref name=mashing/><ref name=kall/> The following rests are potentially useful for modern malts:'''<ref name=kunze/><ref name=sacher/><ref>Visser MJ. [https://core.ac.uk/download/pdf/37326474.pdf Evaluation of malted barley with different degrees of fermentability using the Rapid Visco Analyser (RVA).] University of Stellenbosch. 2011.</ref>
*'''Saccharification rest''' at 142–149°F (61–65°C) - The main purpose of this rest is promoting [[starch]] degradation (by β-amylase and limit dextrinase) in order to produce wort with excellent fermentability. Generally, around 30 minutes is adequate to obtain the increased fermentability and extraction benefits from the saccharification rest, although a longer rest may sometimes be useful depending on the malt and the crush.<ref name=fix/><ref>Rübsam H, Gastl M, Becker T. [https://onlinelibrary.wiley.com/doi/full/10.1002/jib.69 Determination of the influence of starch sources and mashing procedures on the range of the molecular weight distribution of beer using field-flow fractionation.] ''J Inst Brew.'' 2013;119(3):139–148.</ref><ref name=mashing/>
*'''Glycoprotein rest''' at 158–162°F (70–72°C) - The main purpose of this rest is promoting extraction of [[glycoproteins]], which enhance foam, mouthfeel, and flavor stability.<ref name=sacher/><ref name=esslinger/> Some additional starch is extracted, which is degraded by α-amylase.<ref name=langenaekena/><ref name=kuhbeck>Kühbeck F, Dickel T, Krottenthaler M, et al. 
[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> 
*'''Mash-out''' at 167–172°F (75–78°C) - The main purpose of this rest is decreasing the viscosity of the liquid, allowing lautering to proceed more rapidly.<ref name=jinspe/> Additional starch may be gelatinized and degraded during this step as well.<ref name=kunze/> Also, more protein aggregation occurs.<ref name=bsp/> Contrary to popular belief, this step does not "deactivate the enzymes". Temperature is maintained low enough that α-amylase remains active and it continues to degrade any additional starch that becomes gelatinized.<ref name=mulcarb>Muller R. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1991.tb01055.x The effects of mashing temperature and mash thickness on wort carbohydrate composition.] ''J Inst Brew.'' 1991;97(2):85–92.</ref> Other enzymes are active as well, such as peroxidases.

{| class="wikitable" style="float:right; margin-left: 10px;"
|+Step mash schedule<br />(Brewing Forward Hoch-Kurz):
|-
|
<ol>
<li style="margin-left:-20px; margin-right: 10px;">147°F (64°C) for 25 minutes</li>
<li style="margin-left:-20px; margin-right: 10px;">162°F (72°C) for 30 minutes</li>
</ol>
|}
We recommend to mash at 147°F (64°C) for 25 minutes followed by 162°F (72°C) for 30 minutes. A mash-out step is omitted because a boost to lautering speed is usually not needed, and therefore the mash-out merely increases the potential for oxidation ([https://en.wikipedia.org/wiki/KISS_principle KISS]). This mash schedule can be adjusted based on your needs. For example, a staggered saccharification rest (e.g. 144°F [62°C] for 15 minutes followed by 149°F [65°C] for 10 minutes) may be helpful to increase attenuation and extraction, especially for malts with a relatively high gelatinization temperature.<ref name=adb/><ref>Sacher B, Becker T, Narziss L. [http://www.themodernbrewhouse.com/wp-content/uploads/2017/04/pddvxvf.pdf Some reflections on mashing – Part 2.] ''Brauwelt International.'' 2016;6:392-397.</ref><ref name=assessing/><ref>[http://www.themodernbrewhouse.com/forum/viewtopic.php?f=4&t=1519 Musings on mashing.] The Modern Brewhouse website. 2019–2020.</ref> If you use a RIMS or HERMS, another option is to mash-in at a slightly lower temperature such as 131–140°F (55–60°C) and then immediately begin to heat up to the first rest, which can help improve the starch extraction.<ref name=adb/><ref name=iyumad>Iyuke SE, Madigoe EM, Maponya R. [https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2050-0416.2008.tb00773.x The effect of hydroxycinnamic acids and volatile phenols on beer quality.] ''J Inst Brew.'' 2008;114(4):300–305.</ref> However, be aware that mashing-in lower than 140°F (60°C) can increase undesirable oxidation of [[lipids]] (even with low oxygen brewing).<ref name=arts/>

=== Step mashing methods (how to heat the mash) ===
It is important for the temperature to be uniform throughout the mash, otherwise [[starch|saccharification]] time and [[lautering]] time may be extended, and [[efficiency]] may be reduced.<ref name=kunze/> There are two basic ways to heat the mash: multiple infusions, or a recirculating system that heats the wort.

'''Multiple infusions'''<br />
A low-tech way to increase mash temperature is to add a controlled amount of boiling water. With this multiple-infusion method, the mash starts out relatively thick since it becomes thinner as water is added for each step. Therefore, the strike water volume typically needs to be lower since more water is added later. In order to ensure that the heat is evenly distributed, the mash should be stirred after adding the water. Also, preventing heat loss is important for accurately hitting the rest temperatures. Software can be used to determine the amount of boiling water required to increase the temperature for each step, such as the 
[https://www.brewersfriend.com/mash/ "Mash Infusion, Strike Water, and Rest Schedule Calculator" at Brewer's Friend]<!-- or [https://www.rackers.org/calcs.shtml Rackers] (broken link)-->. You need to know your elevation to use the calculator because the temperature of boiling water changes based on elevation. Also be aware that you may need to use slightly more water in order to make up for heat losses.<!-- Does the calculator account for thermal expansion? Should I make my own calculator? -->

'''Recirculating systems'''<br />
There are several types of mashing systems that use electric pumps to move wort from the bottom of the mash vessel back to the top. There must be a "false bottom" in the vessel to keep the grain suspended above the outflow. Recirculation mixes the wort to ensure that the temperature is fairly even throughout the mash. These systems heat the wort either directly or indirectly while circulating (circulating ''without'' heating will cause a significant drop in temperature). Besides controlling mash temperature, another benefit is that these systems produce very clear wort going into the boil.<ref name=bsp/> The drawbacks to these systems are the higher equipment cost and system complexity, higher [[shear]] force, and an increased risk of a stuck mash (especially with traditional high-oxygen brewing). Although, once they are set up, they can make step mashing quite easy. Depending on the system, the brewer may simply need to enter the desired mash temperature, and the system steadily heats to the target. Systems can also be built to fully automate the step mashing process, which allows very high consistency from one brew to the next.

Some notes about recirculation:<br />
The grain husks form a grain bed in the mashing vessel, allowing wort and sparge liquor to flow through it. This is where fine particles are filtered out, not at the false bottom, which only acts as a support.<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><ref name=kall/> Recirculation thus gives maximum extraction and improved clarity of the wort.<ref name=whitting>Whitting C. [https://www.beerandbrewer.com/milling-your-grain/ Milling your grain.] Beer & Brewer. 2018. Accessed 2020.</ref> Clear wort contains the lowest levels of [[lipids]]. This is beneficial because lipids negatively affect [[foam|foam stability]] and [[flavor stability]], particularly when [[oxidation|oxidized]].<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>

Under [[oxidation|oxidizing]] conditions, fine aggregates of [[protein]], small [[starch]] granules, cell wall polysaccharides ([[beta-glucans and arabinoxylans]]), and [[fatty acids|lipids]] can form a gel-like layer (in German: ''Oberteig'' or ''Schmutzdecke'') on the surface of the grain bed, which limits flow.<ref name=bsp/><ref name=jinspe>Jin YL, Speers RA, Paulson AT, Stewart RJ. [https://www.researchgate.net/profile/Robert-Speers/publication/285959138_Effects_of_b-Glucans_Shearing_and_Environmental_Factors_on_Wort_Filtration_Performance/links/587e215408ae4445c06f6ff2/Effects-of-b-Glucans-Shearing-and-Environmental-Factors-on-Wort-Filtration-Performance.pdf Effects of β-glucans, shearing, and environmental factors on wort filtration performance.] ''J Am Soc Brew Chem.'' 2004;62(4):155–162.</ref><ref name=whitting/> Therefore [[low oxygen brewing|preventing oxygen]] in the mash reduces the formation of this gel layer and increases the wort flow rate during recirculation, reducing the likelihood of a [[stuck mash]].<ref name=bsp/><ref name=hob/> Wort flow rate can be also be improved by proper [[milling]], proper [[brewing pH|pH control]], and increased [[calcium]] ion concentration during mashing.<ref name=hob>Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. [[Library|''Handbook of Brewing.'']] 3rd ed. CRC Press; 2017.</ref> Mashes that include huskless grains such as [[wheat]] or [[rye]] malt, or [[oats|oat]] flakes are especially problematic with regard to a potential stuck mash. Along with measures already mentioned, one way to avoid difficulty is to increase the permeability of the mash bed by adding [[rice hulls]].<ref>Miller D. [http://brewlikeapro.net/maltmilling.html Mills and milling.] Brew Like A Pro website. 2012. Accessed 2020.</ref>

== Preventing oxidation ==
Traditional brewing methods allow a huge amount of oxygen into the wort during mashing, and this oxygen reacts very rapidly with wort components,<ref name=mullerr/><ref name=kanbam/><ref name=bamenz>Bamforth CW. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1999.tb00025.x Enzymic and non‐enzymic oxidation in the brewhouse: A theoretical consideration.] ''J Inst Brew.'' 1999;105(4):237–242.</ref> a chemical process called oxidation. Oxidation causes many negative effects including loss of fresh grain flavor, and development of off-flavors including harsh bitterness, astringency, and the potential for cardboard flavors that can show up during beer storage. Oxidation during this stage also causes a loss of natural [[antioxidants]], which are important for [[flavor stability]] (including preservation of hop aroma). See [[Oxidation]] for a detailed discussion of all the negative effects of oxidation and how it occurs.

In order to produce high-quality beer, steps can be taken to avoid oxidation during mashing; these methods are often referred to as ''low oxygen brewing'' or ''LODO''. To successfully realize the full array of benefits from minimizing oxidation during mashing, the process should utilize low-oxygen methods at every step in the [[brewing]] process starting with raw ingredient selection and ending with storage and dispensing. See [[low oxygen brewing]] for an overview of methods to avoid the damaging effects of oxidation.

{| class="wikitable"
|+ Mash Oxidation Prevention Guide
|-
!Source of oxygen or catalysts !! Steps needed to avoid oxidation
|- style="vertical-align:top;"
| [[Water]] used for mash-in contains dissolved oxygen.<ref name=kanbam>Kanauchi M, Bamforth CW. [https://www.themodernbrewhouse.com/wp-content/uploads/2019/02/BrewingScience_bamforth_82-84.pdf A Challenge in the study of flavour instability.] ''BrewingScience - Monatsschrift Brauwiss.'' 2018;71(Sept/Oct):82–84.</ref>
|
* [[Remove dissolved oxygen from water|Remove the dissolved oxygen]] using "yeast oxygen scavenging", nitrogen sparging, a membrane system, or other deaeration method.<ref name=mullerr/><ref name=bie/>
|- style="vertical-align:top;"
| Many pockets of air are entrained in the grist after [[milling]], which transfer oxygen to the wort upon mash-in.<ref name=kanbam/><ref name=kall/>
|
* Flush the grist with inert gas before mash-in.<ref name=mullerr/> This is typically accomplished by adding the grain to the mash vessel and flushing it with CO<sub>2</sub> or N<sub>2</sub> from below for a few minutes before mash-in.<ref name=mullerr/>
* Underlet the water during mash-in, i.e. add the water gently from the bottom of the mash vessel.
|- style="vertical-align:top;"
| Oxygen diffuses into the wort wherever the wort contacts air.<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 name=golston/><ref name=kanbam/>
|
* If possible, replace the air in the mash vessel with nitrogen.<ref name=mullerr/><ref name=bie/><ref name=kanbam/><ref name=arakim>Araki S, Kimura T, Shimizu C, Furusho S, Takashio M, Shinotsuka K. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-57-0034 Estimation of antioxidative activity and its relationship to beer flavor stability.] ''J Am Soc Brew Chem.] 1999;57(1):34–37.</ref><ref name=frefes>Frederiksen AM, Festersen RM, Andersen ML. [https://pubs.acs.org/doi/abs/10.1021/jf801666e Oxidative reactions during early stages of beer brewing studied by electron spin resonance and spin trapping.] ''J Agric Food Chem.'' 2008;56(18):8514–8520.</ref> Alternately, a "mash cap" can be used to greatly reduce the amount of wort surface exposed to the air. This is especially important for small-scale brewing, where there is a much greater surface area relative to the volume of wort.<ref name=bie>Biering J. [https://www.asbcnet.org/events/archives/2017ASBCMeeting/proceedings/2017Proceedings/22_Biering.pdf Reliable scale up/scale down in process development—New possibilities to close the gap between lab, pilot brewery, and industrial scale.] Slides presented at: ''Annual meeting of American Society of Brewing Chemists.'' June 4–7, 2017; Fort Myers, FL.</ref><ref name=kall/>
* Minimize the amount of stirring, splashing, and agitation.<ref name=mullerr/><ref name=golston/><ref name=adb/><ref name=kanbam/> This includes pumping gently, minimizing the amount of recirculation, and minimizing the number of transfers.<ref name=mullerr/><ref name=golston/><ref name=kanbam/> However, a short and gentle stir after mash-in is a fine practice, and might be better than not stirring at all.<ref name=arakim/>
* Limit mashing duration to 1–2 hours.<ref name=kunze/><ref name=adb/>
* Flush tubing, pumps, etc. with inert gas before running wort or brewing water through them.
* Avoid using a BIAB system for lautering, because it causes a lot of air exposure when the grain bag is removed. Avoid all-in-one systems for the same reason, and they are typically not designed for minimizing agitation/splashing.
|- style="vertical-align:top;"
| The grain contains [[transition metals]], [[enzymes]], and other materials that promote oxidation (catalysts).<ref name=mullerr/>
|
* Use antioxidant additives in the mash, especially [[tannin additives]] and [[sulfite]].
* Mash-in at 144°F (62°C) or higher.<ref name=mullerr/><ref name=adb/>
* Control mash pH and acid/base.
* Circulation is helpful to improve wort clarity, reducing the amount of oxidized lipids carried forward to the boil kettle.
|- style="vertical-align:top;"
| Oxygen diffuses through [[plastic]]s, into the wort.
|
* Avoid plain silicone tubing.
|}

== Quality assurance and monitoring ==
The progress and status of mash chemistry can be tested to ensure that a high-quality wort is being produced.

* '''Measure mash pH''' - Mash pH should be checked to verify that is it at the target value. Proper pH control during mashing is beneficial for optimal activity of various [[enzymes]], improving the extraction of [[zinc]], and other important effects. Furthermore, the mash pH carries forward to the [[boiling|boil]] and [[fermentation]], where pH control has additional benefits. See [[Brewing pH]]. If the pH has not successfully been controlled (i.e. the pH is not at target value), brewers generally should NOT try to adjust it during the mash. However, it is recommended to adjust pH going into the boil kettle.
* '''Monitor oxidation''' - [[low oxygen brewing|Low oxygen brewers]] may be interested to track the amount oxidation occurring in the mash (traditional brewers don't need to monitor oxidation, because the mash always becomes heavily oxidized immediately upon mash-in). Unfortunately, wort oxidation is not something that can easily be measured. Low oxygen bewers can monitor for ''excessive'' oxidation simply by looking for changes in color, and tasting the wort to ensure that the fresh grain flavor is still present.<ref name=kall/> Measuring dissolved oxygen levels (with a [[DO meter]]) is not particularly useful since any oxygen dissolved in the wort is consumed by rapidly by oxidation reactions. An [[ORP meter|ORP (Oxidation Reduction Potential) meter]] is potentially useful for monitoring the redox status of the wort, but it is not commonly used in brewing. The most effective way to estimate the amount of oxygen getting into the wort (although not necessarily the amount of oxidation that has occurred) is to add [[sulfite]] and monitor how much is lost during the brewing process. Testing sulfite level is best accomplished by a titration method, see [[SO2 testing|sulfite testing]].
* '''Monitor extract''' - Brewers may periodically measure wort density or refraction (e.g. using a [[hydrometer]] or [[refractometer]]) to track the amount of grain components that have been dissolved into the wort (note that this measures [[extract]]ion of ''all'' wort components, not just starch and sugars).<ref name=gordon>Gordon R, Power A, Chapman J, Chandra S, Cozzolino D. [https://www.mdpi.com/2311-5637/4/4/89/pdf A review on the source of lipids and their interactions during beer fermentation that affect beer quality.] ''Fermentation.'' 2018;4(4):89.</ref> The benefits to monitoring [[extract]] are unclear, so while it may provide interesting information, this practice is generally not needed when brewers are following good methods (proper mash temperature, [[brewing pH|mash pH]], mash duration, [[milling]], etc).
* '''Check for undegraded starch''' - [[Starch]] that hasn't been adequately broken down during mashing can cause [[haze]] in beer. Therefore, an [[iodine test]] can be used at the end of mashing to help identify whether starch is the source of haze in a hazy beer. When used, it should be conducted again at the end of the [[boiling|boil]]. Iodine testing is typically not needed on a regular basis.

== See also ==
* [[Home brewing systems]]
* [[Water]]
* [[Lautering]]

== References ==
[[Category:Wort production]]