A close-up view of grains steeping in warm water during the mashing stage of brewing.

In brewing and distilling, mashing is the process of combining a mix of milled grain (typically malted barley with supplementary grains such as corn, sorghum, rye or wheat), known as the "grain bill", and water, known as "liquor", and heating this mixture. Mashing allows the enzymes in the malt to break down the starch in the grain into sugars, typically maltose to create a malty liquid called wort.[1] There are two main methods—infusion mashing, in which the grains are heated in one vessel; and decoction mashing, in which a proportion of the grains are boiled and then returned to the mash, raising the temperature.[2] Mashing involves pauses at certain temperatures (notably 45–62–73 °C or 113–144–163 °F), and takes place in a "mash tun"—an insulated brewing vessel with a false bottom.[3][4][5] The end product of mashing is called a "mash".


The term "mashing" probably originates from the Old English noun masc, which means "soft mixture", and the Old English verb mæscan which means "to mix with hot water". The term's use to refer to "anything reduced to a soft pulpy consistency" is recorded as early as the late 16th century.[6]

Infusion mashing

Most breweries use infusion mashing, in which the mash is heated directly to go from rest temperature to rest temperature. Some infusion mashes achieve temperature changes by adding hot water, and there are also breweries that do single-step infusion, performing only one rest before lautering.

Decoction mashing

Decoction mashing is where a proportion of the grains are boiled and then returned to the mash, raising the temperature. The boiling extracts more starch from the grain by breaking down the cell walls of the grain. It can be classified into one-, two-, and three-step decoctions, depending on how many times part of the mash is drawn off to be boiled.[7] It is a traditional method, and is common in German and Central European breweries.[8][9] It was used out of necessity before the invention of thermometers allowed simpler step mashing. But the practice continues for many traditional beers because of the unique malty flavor it lends to the beer; boiling part of the grain results in Maillard reactions, which create melanoidins that lead to rich, malty flavours.[10]

Mash tun

Interior view of a mash tun in a Scotch whisky distillery, showing the stirring mechanism.
An empty mash tun showing the integrated mash rake.

In large breweries, in which optimal utilization of the brewery equipment is economically necessary, there is at least one dedicated vessel for mashing. In decoction processes, there must be at least two. The vessel has a good stirring mechanism, a mash rake, to keep the temperature of the mash uniform, and a heating device that is efficient, but will not scorch the malt (often steam), and should be insulated to maintain rest temperatures for up to one hour. A spray ball for clean-in-place (CIP) operation should also be included for periodic deep cleaning. Sanitation is not a major concern before wort boiling, so a rinse-down should be all that is necessary between batches.

Smaller breweries will often use a boil kettle or a lauter tun for mashing. The latter case either limits the brewer to single-step infusion mashing or leaves the brewer with a lauter tun that is not completely appropriate for the lautering process.


Mixing of the strike water, water used for mashing in, and milled grist must be done in such a way as to minimize clumping and oxygen uptake. This was traditionally done by first adding water to the mash vessel, and then introducing the grist from the top of the vessel in a thin stream. This has led to a lot of oxygen absorption, and loss of flour dust to the surrounding air. A premasher, which mixes the grist with mash-in temperature water while it is still in the delivery tube, reduces oxygen uptake and prevents dust from being lost.

Mashing in (sometimes called "doughing-in") is typically done between 35 and 45 °C (95 and 113 °F), but, for single-step infusion mashes, mashing in must be done between 62–67 °C (144–153 °F) for amylases to break down the grain's starch into sugars. The weight-to-weight ratio of strike water and grain varies from 12 for dark beers in single-step infusions to 14 or even 15, ratios more suitable for light-colored beers and decoction mashing, where much mash water is boiled off.

Enzymatic rests

Optimal rest temperatures for major mashing enzymes
Temp °C Temp °F Enzyme Breaks down
40–45 °C 104.0–113.0 °F β-Glucanase β-Glucan
50–54 °C 122.0–129.2 °F Protease Protein
62–67 °C 143.6–152.6 °F β-Amylase Starch
71–72 °C 159.8–161.6 °F α-Amylase Starch

In step-infusion and decoction mashing, the mash is heated to different temperatures at which specific enzymes work optimally. The table at right shows the optimal temperature ranges for the enzymes brewers pay the most attention to and what material those enzymes break down. There is some contention in the brewing industry as to just what the optimal temperature is for these enzymes, as it is often very dependent on the pH of the mash, and its thickness. A thicker mash acts as a buffer for the enzymes. Once a step is passed, the enzymes active in that step are denatured by the increasing heat and become permanently inactive. The time spent transitioning between rests is preferably as short as possible; however, if the temperature is raised more than 1 °C per minute, enzymes may be prematurely denatured in the transition layer near heating elements.

β-Glucanase rest

β-glucan is a general term for polysaccharides, such as cellulose, made up of chains of glucose molecules connected by beta glycosidic bonds, as opposed to alpha glycosidic bonds in starch. These are a major constituent of the cell wall of plants, and make up a large part of the bran in grains. A β-glucanase rest done at 40 °C (104 °F) is practiced in order to break down cell walls and make starches more available, thus raising the extraction efficiency. Should the brewer let this rest go on too long, it is possible that a large amount of β-glucan will dissolve into the mash, which can lead to a stuck mash on brew day, and cause filtration problems later in beer production.

Protease rest

Protein degradation via a proteolytic rest plays many roles: production of free-amino nitrogen (FAN) for yeast nutrition, freeing of small proteins from larger proteins for foam stability in the finished product, and reduction of haze-causing proteins for easier filtration and increased beer clarity. In all-malt beers, the malt already provides enough protein for good head retention, and the brewer needs to worry more about more FAN being produced than the yeast can metabolize, leading to off flavors. The haze causing proteins are also more prevalent in all-malt beers, and the brewer must strike a balance between breaking down these proteins, and limiting FAN production.

Amylase rests

The amylase rests are responsible for the production of free fermentable and nonfermentable sugar from starch in a mash.

Starch is an enormous molecule made up of branching chains of glucose molecules. β-amylase breaks down these chains from the end molecules forming links of two glucose molecules, i.e. maltose. β-amylase cannot break down the branch points, although some help is found here through low α-amylase activity and enzymes such as limit dextrinase. The maltose will be the yeast's main food source during fermentation. During this rest starches also cluster together forming visible bodies in the mash. This clustering eases the lautering process.

The α-amylase rest is also known as the saccharification rest, because during this rest the α-amylase breaks down the starches from the inside, and starts cutting off links of glucose one to four glucose molecules in length. The longer glucose chains, sometimes called dextrins or maltodextrins, along with the remaining branched chains, give body and fullness to the beer.

Because of the closeness in temperatures of peak activity of α-amylase and β-amylase, the two rests are often performed at once, with the time and temperature of the rest determining the ratio of fermentable to nonfermentable sugars in the wort and hence the final sweetness of the fermented drink; a hotter rest gives a fuller-bodied, sweeter beer as α-amylase produces more unfermentable sugars. 66 °C (151 °F) is a typical rest temperature for a pale ale or German pilsener, while Bohemian pilsener and mild ale are rested more typically at 67–68 °C (153–154 °F).

Decoction "rests"

In decoction mashing, part of the mash is taken out of the mash tun and placed in a cooker, where it is boiled for a period of time. This caramelizes some of the sugars, giving the beer a deeper flavor and color, and frees more starches from the grain, making for a more efficient extraction from the grains. The portion drawn off for decoction is calculated so that the next rest temperature is reached by simply putting the boiled portion back into the mash tun. Before drawing off for decoction, the mash is allowed to settle a bit, and the thicker part is typically taken out for decoction, as the enzymes have dissolved in the liquid, and the starches to be freed are in the grains, not the liquid. This thick mash is then boiled for around 15 minutes, and returned to the mash tun.

The mash cooker used in decoction should not be allowed to scorch the mash, but maintaining a uniform temperature in the mash is not a priority. To prevent a scorching of the grains, the brewer must continuously stir the decoction and apply a slow heating.

A decoction mash brings out a higher malt profile from the grains and is typically used in Bocks or Doppelbock-style beers.


After the enzyme rests, the mash is raised to its mash-out temperature. This frees up about 2% more starch, and makes the mash less viscous, allowing the lauter to process faster. Although mash temperature and viscosity are roughly inversely proportional, the ability of brewers and distillers to use this relationship is constrained by the fact that α-Amylase quickly denatures above 78 °C (172.4 °F). Any starches extracted once the mash is brought above this temperature cannot be broken down, and will cause a starch haze in the finished product, or in larger quantities an unpleasantly harsh flavor can develop. Therefore, the mash-out temperature rarely exceeds 78 °C (172.4 °F).

If the lauter tun is a separate vessel from the mash tun, the mash is transferred to the lauter tun at this time. If the brewery has a combination mash-lauter tun, the agitator is stopped after mash-out temperature is reached and the mash has mixed enough to ensure a uniform temperature.

See also


  1. Ensminger, Audrey (1994). Foods & Nutrition Encyclopedia, 2nd Edition, Volume 1. CRC Press. p. 188. ISBN 0849389801. Retrieved 2016-03-02.
  2. Rabin, Dan; Forget, Carl (1998). The dictionary of beer and brewing. Taylor & Francis. p. 180. ISBN 1579580785. Retrieved 2016-03-02.
  3. "Abdijbieren. Geestrijk erfgoed" by Jef Van den Steen
  4. Bier brouwen
  5. What is mashing?
  6. Harper, Douglas. "Mash". Online Etymology Dictionary. Retrieved 2016-03-04.
  7. Briggs, D.E.; Hough, J.S. (1981). Malting and Brewing Science: Malt and Sweet Wort. Springer Science & Business Media. p. 330. ISBN 0-412-16580-5. Retrieved 2016-03-02.
  8. Briggs, D.E. (1998). Malts and malting. Springer Science & Business Media. p. 233. Retrieved 2016-03-02.
  9. Briggs, D.E.; Hough, J.S. (1981). Malting and Brewing Science: Malt and Sweet Wort. Springer Science & Business Media. p. 3. Retrieved 2016-03-02.
  10. Decoction Mashing
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