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The Importance of Controlling Mash Temperature

The Importance of Controlling Mash Temperature

The mash is the first enzymatic step completed during the brew day. Where we re-activate the germination enzymes that the barleycorn uses for a new seedling by taking the kilned malt and steeping with warm water. Proper malting helps pause these enzymes and preserves them for when they finally reach the brewhouse.

The overall purpose is to continue the germination process and convert the complex starches of the seed by using the enzymes stored in the bran. The starches are divided by the amylases into shorter branches so that the yeast can consume them in the fermentation.

Types of Mashing Enzymes

Table 1 - Main Groups of Mashing Enzymes

What happens during mashing?

The beginning of the brewing process, when crushed grains are blended with water to make a porridge-like substance known as the "mash," is referred to as mashing. Malt and other cereal starches are converted to sugars, proteins, and other components in the mash, resulting in the sweet fermentable liquid known as wort. Malt is delivered in entire kernels from the malting building to the brewery. First, it is processed into the grain mixture known as "grist." Next, the grain is combined with precisely measured amounts of warm or hot water. Infusion mashing, decoction mashing, and temperature-controlled infusion mashing are the three primary types of mashing processes. Mashing is converting the long-chain starches of the barley kernel into the small chain sugars needed by yeast to make alcohol. When the crushed grain gets wet with water at the proper temperature, the starches and enzymes liquefy into the mash, where the conversion starts. Depending on local tradition, the quality of malt available, the equipment utilised, and the brewed beer, different mashing procedures are employed in other parts of the world.

The Protein Rest

The protein of the grain can be found throughout the barleycorn. Well-modified malts already have some of the proteins broken down to a level that is favourable for brewing. The two main protein eating enzymes are peptidase and protease. Peptidase breaks down peptides to create amino acids that are needed by the yeast during fermentation; protease cleaves large proteins to help provide more head stability and reduce haze from the grain.
The protein rest occurs at a lower temperature than the saccharification rest. With most grain bills using malted barley, this step can be skipped, resulting in a light beer. However, when using large amounts of unmalted or flaked grains, including raw barley, wheat, rye, or oats, this step can help reduce the mash's overall protein content. In general, with flaked grains, the protein rest will improve lauter filtration, head retention, and overall beer clarity.
The other reason to perform this rest is to help combat β-glucans. The glucan semi-celluloses from β-glucans give doughs and porridges their elastic properties, which will slow lauter speeds. Therefore, this step should only be administered when it is possible to heat the mash tun. Otherwise, temperature stable bacterial-derived enzymes are commercially available, which can mean this rest can be skipped.

The Saccharification Rest

The primary purpose of the mash is to convert the long-chain starches of the barleycorn into short-chain sugars. Starch comes in two primary forms: amylose and amylopectin. Amylose is a long straight chain of repeating sugars. Amylopectin is made up of many-branched chains. There are two primary enzymes responsible for the conversion of starches to sugars: β-amylase and α-amylase.

Beta Amylase (β-amylase)

β-amylase works by breaking apart the starches at the ends of the chains; it consistently forms maltose during this conversion. However, since it can only operate at the tips of the starches, it needs a fair amount of time to work and leaves larger dextrins when converting amylopectin. It works best at lower temperatures, and higher temperatures tend to denature this enzyme.

Alpha-Amylase (α-amylase)

α-amylase works by cleaving starches in the middle of the chains, but the lengths will be inconsistent. This allows for β-amylase to have more ends of the starches to convert into maltose. α-amylase also can work on either amylose or amylopectin and can make smaller dextrins when converting amylopectin. Generally, it works better at slightly higher temperatures as it is more temperature stable than β-amylase. By balancing the saccharification rest temperature, we can alter the eventual fermentability of the wort.

How to Use Mash Temperature to Help Balance Body

Figure 1 - Starch Liquification Temperatures (Briggs, et al., 2004)

The first step when it comes to mashing is to set an ideal mash temperature. The primary concern is that the starches will liquefy or dissolve in the water at the appropriate setpoint. Using an all-malt grist of barley tends to be overlooked as the starch liquefaction temperatures are like the starch conversion temperatures. Wheat, rye, and oats have similar properties. Still, rice and corn do not liquify at typical mashing temperatures and require a separate cereal mash or flaked before brewing.

Most mashes will have an overall rest of 63 – 69 °C (145 – 156 °F). A lower mash temperature will favour the β-amylase and produce a more fermentable wort. A higher mash temperature will select the α-amylase and produce a wort with more dextrins. Picking a temperature for your beer will help determine the final body. Lower starting gravity beers typically benefit from a moderate or high mash temperature due to the small grain bills; table strength beers usually benefit from a low or average mash temperature. Imperial strength beers typically benefit from a low mash temperature. The final sugar levels will help balance flavours from hops, alcohol, and overall drinkability. Lower mash temperatures will have a lighter body, a drier mouthfeel, and a milder flavour.

Types of Brewery Mashes

Single Infusion

Single infusion is the most straightforward method of mashing. Typically, the heat capacity of the grain is taken into consideration, and hot water and the grist are mixed to land at the desired mash temperature. The strike water will be at a higher temperature than the mash to compensate for the lower temperature of the grain. The mash tun should be insulated or have an external heating source to keep the temperature constant for the mash duration. This option is terrific for well-made malts. Water temperature is easy to control by adding either hot or cold water.


This is where several different rests occur in succession. First, the strike water is heated to a level where the grist will reach the initial rest temperature, such as a protein rest. Once the rest is complete, the mash is heated by adding additional hot water or an external heat source to raise the temperature to the next rest level. Mixing with a mash paddle or a mechanical agitator is recommended to ensure a consistent temperature throughout the mash. This setup is more familiar with unmalted grains to ensure that the starches liquefy and are converted at the appropriate levels. Cereal mashes of rice or corn are also a type of multi-step mash. Multi-step mashes give the brewer much control over the final wort. Still, they can be challenging to do in combination with mash lauter tuns.

Decoction Mash

A decoction mash was initially developed to compensate for historic malting techniques. The mash is set at a series of rest temperatures, and a portion of that grist is strained to remove any grain solids. The liquid is heated in a secondary vessel to boiling. The boiling destroys any enzymes but produces complex malt and caramel flavours through Maillard reactions. This liquid is reintroduced back into the mash, causing the average temperature to increase. While the standard for hundreds of years, advancements in malting procedures have made decoction mashes uncommon. The challenges have moved from the brewer to the maltster. This type of mashing can be found in German brewing styles, and many brewers still swear by the results.

What happens if you miss your mash temperature?

Unfortunately, suppose you miss your mash temperature. In that case, you will either get a wort without converted sugars or a wort that will have too many unfermentable sugars. A low temperature will risk the starches not liquifying or converting, not giving the yeast the food they need to make alcohol. Using a strike temperature calculator is a helpful tool to get your mash temperature dialled in every time.

When the mash is too cold, you need to figure out a way to add energy to the mash, without the proper temperature range, incomplete conversions or stuck lauters can be a result.

Low Mash Temperature Fixes

  1. Add additional hot water.
  2. Direct heating.
  3. Decoction mashing.

They all have advantages and disadvantages. The addition of hot water is simple and quick, but it can dilute the water to grain ratio, diluting the concentration of enzymes. Furthermore, your vessel may not have the space needed to raise the temperature high enough!

Direct heating is where either an element, a burner, or steam is used to heat up the temperature of the vessel entirely. These are easier on smaller systems since the heat load of the mash is so little, when there is more malt, much more heat needs to be applied. Additionally, it is almost impossible to heat lauter tuns since the runoff ports make it difficult to heat without scorching and the lauter rakes are not compatible with accurate temperature sensors for controlling the heat.

Using decoction mashing is a method of performing multi-step mashes without the need for extra water or heat in the Mash Tun. It entails transferring approximately a third of the Mash to another pot, heating it to conversion temperature, and then boiling it. This method meets three goals: adding boiling hot strained sweet wort to the main mash elevates the temperature of the mash to the next resting temperature, with moderately modified continental malts it results in a higher degree of extraction, and it enables the crisp, dry maltiness typical of Munich-style lagers.

High Mash Temperature Fixes

  1. Add additional cold water.
  2. Use a heat exchanger.

Adding cold water is a quick and easy way to lower the mashing temperature of the mash. Stirring vigorously with the addition of cold water from either a city line or a cold liquor tank will help a lot faster to lower the temperature than trying to raise the temperature with hot water. Coldwater has a lot of thermal loading potential when compared to hot water and there are fewer risks of tannin extraction. Just be sure to use water that has had the chlorine removed and is at the proper mineral content.

The other method is to use a heat exchanger that is connected to cooling water or glycol. Nano-sized systems can use an immersion chiller while larger systems will need a shell and tube or plate and frame heat exchanger. Be sure to keep in mind that chilling the wort at this phase too quickly may cause pumping issues since the wort has not had a hot protein break and will be more viscous than boiled wort. Another area for concern is to not overcorrect too quickly, as having to heat the mash again can be complicated after adding so much water.

How to Check Mashing is Complete

The most common method for determining the completion of a mash is to use iodine. Typical pharmacy iodine works well for this test. A sample of the wort is collected, strained, and placed in a small dish or cup, a dash of iodine is added to the side of the sample, and a little bit of the wort is swirled to the iodine. If starches are present, the iodine will turn pitch black. Otherwise, it will be a mellow brown colour. This test will help ensure that the conversion has been completed and the starches have been converted to sugars. It can be more challenging to use this test with turbid mashing styles common in Lambic breweries or grain-based distilleries.  

Importance of a Mash Mixer over a Mash Tun

Temperature control is the essential factor for proper mashing procedures. However, using only a mash tun for conversion at larger scales can be difficult to control temperatures or fix incorrect strike water temperatures accurately. Unfortunately, once a craft brewery becomes a specific size, it is impossible for the mashing to be done by hand and rakes and plough systems need to be used. In addition, a typical lauter tun is very difficult to heat appropriately since the rakes' temperature sensors would get damaged, and the jackets can scorch the mash under the false bottom.

For breweries 20bbl and up, a mash mixer is recommended. This gives the brewer control over specific mash temperatures, is able to correct strike water problems, and have more detailed mashing profiles at the same time. It also allows for the lauter tun to be turned over faster, helping complete more brews in a single day. The multi-step process has many more benefits than listed here and will help make your beers taste fantastic.

Works Cited

Briggs, D. E., Brookes, P. A., Stevens, R. & Boulton, C. A., 2004. Brewing: Science & Practice. Cambridge: Elsevier Science & Technology.

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