Correct Mash Temperature (Impact of incorrect mash temperatures) 

During the mashing process, malted barley is steeped in hot water so that enzymes can break down the starch in the grains and convert them into sugar. The mash temperature affects the amount and type of sugars extracted and ultimately, the style and flavour of the finished beer.

The correct temperature for infusion mashing is between 63 and 70 ºC (145 and 158 Fahrenheit). Mash temperatures at the lower end of this range produce more fermentable sugar and stronger beers. Higher temperatures produce more non-fermentable sugars and sweeter, fuller-bodied beers.

If you mash below this temperature range, you will extract fewer sugars and end up with watered-down beer. Mash temperatures higher than 70ºC (158 Fahrenheit) will kill the enzymes and prevent them from converting the available starch into sugar.

At the end of the day, less fermentable sugar in the wort means less alcohol in your beer.

An insulated picnic cooler like this one helps maintain the correct mash temperature
Picnic coolers make good mash tuns because the insulation helps maintain the correct mash temperature

What happens during the mashing process?

Conversion of starch into sugars

Barley is made up of around 60% starch molecules. During the mashing process, enzymes in the barley (alpha and beta-amylase) break down the starch molecules and convert them into sugars.

The conversion takes place in two stages or steps.

First, the starch molecules have to be dissolved in water. The starch molecules in barley become soluble at temperatures higher than 60ºC (140 ºF).

Next, the long-chain starch molecules are broken down by the enzymes and converted into different sugar types.

Brewer’s yeast can only ferment short-chain sugars (maltose and dextrose) which are referred to as fermentable sugars. Other, longer chain sugars are called dextrins and, since they can’t be fermented, add sweetness and body to your beer.

Alpha-amylase breaks starch molecules down into mostly non-fermentable sugars and is most active between 67 and 75ºC (153 to 167 Fahrenheit).

Beta-amylase breaks the starch molecules down into fermentable sugars, mostly maltose and is most active between 55 and 65ºC (131 to 149 Fahrenheit).

As a general rule, mashing at temperatures between 63 and 65 ºC (145 – 159 ºF) results in a dryer, stronger beer. Whereas, a mash temperature between 66 and 68ºC will yield a more full-bodied beer or ale.

Proteins and amino acids

In addition to alpha and beta-amylase, there are other enzymes present in barley which break down complex, long-chain, proteins into medium-chain proteins and amino acids.

These shorter chain proteins are water-soluble, add body to the finished beer and help nourish the yeast during fermentation. The protein content in beer is also responsible for creating a lasting foamy head.

Although most of the protein conversion occurs during the malting process, some types of malt may benefit from a so-called protein rest at temperatures between 45 and 55ºC (113 – 131 Fahrenheit).

Malt flavours

There are more than twenty different varieties of malt to choose from, and most beer recipes require a combination of two or more of them. During the mashing process, each malt adds its own unique flavour and character to the wort.

Tannins and polyphenols

Tannins (aka polyphenols) are an organic compound found in the husk of barley seeds and the strigs of hops. They are present in beers and wines and add bitterness, they also react with proteins in the wort during the boil, casing the hot break.

Tannins seep out of the barley during the mashing and sparging processes. The quantity of tannins present is dependent on a combination of acidity and temperature.

The quantity of tannins released increases dramatically at temperatures higher than 77ºC (171 Fahrenheit). This isn’t usually a problem during mashing but can be an issue when sparging.

Methods and styles of mashing

Over the centuries, three distinct methods of mashing have evolved based on the styles of beers produced and the types of malt being used.

Infusion Mashing

Infusion mashing involves heating the entire mash to a predefined temperature and holding it there for a set period of time.

Step Mashing

Step mashing is similar to infusion mashing. The difference is that in step mashing the mash is heated to a series of temperatures called rests.

The theory behind step mashing is that each of the rests will release different sugars and proteins from the malt, creating a more complex and balanced beer.

Decoction mashing

Decoction mashing is similar to step mashing except that, instead of heating the entire mash, part of the mixture is removed from the mash tun. It is then boiled before being mixed back into the main mash.

In the past, most brewers used to use the decoction mash process. Nowadays, thanks to the modern highly modified malts currently available, most brewers mash at just one temperature.

Mixing the mash in a small converted picnic cooler
Gently stir the mash as you add the grain to prevent dough balls

Temperatures used for Multi-Step and Decoction Mashing

As mentioned earlier, the mashing process allows the different enzymes in barley to go to work converting starch into sugars and breaking down proteins into less complex proteins and amino acids.

Since each of the enzymes is most active at a different temperature, by holding the mash at a series of pre-defined temperatures, an experienced brewer can ensure that each enzyme can go to work under optimum conditions.

Depending on the type of beer being brewed, from three to six temperature rests are used in a process that lasts between one and two hours.

By comparing the tables below, you can see how each rest coincides with the optimum temperature range of one or more enzymes.

Enzyme activity

This table shows the temperatures at which the enzymes involved in mashing are most active.

Enzyme Optimum Temperature Chemical Reation
Alpha amylase 70ºC (158ºF) Breaks down starch into non-fermentable sugars
Beta amylase 64ºC (147ºF) Breaks down starch into fermentable sugars
Beta glucanase 45ºC (113ºF) Breaks down gums which surround starch molecules
Peptidase 50ºC (122ºF) Breaks down complex proteins into simple protiens
Protease 58ºC (136ºF) Breaks down simple proteins into amino acids

Mash rest temperatures

This table shows the most common rest temperatures.

Temperature Rest
35-45°C (95-113°F) Acid rest
44-59°C (113-138°F) Protein rest
61-71°C (142-162°F) Saccharification rest
60–63°C (140–145°F) Beta-amylase rest
66–67°C (150–152°F) Alpha-amylase rest


Mashing techniques used by homebrewers

Most homebrewers perform a single rest infusion mash which entails maintaining a constant mash temperature for about an hour.

Converted picnic coolers make ideal mash tuns for infusion mashing because they are cheap and do a good job maintaining the correct temperature throughout the mashing process.

Another popular method is the so-called Brew in a Bag (BIAB) technique whereby mashing is done in the boil kettle, normally insulated with old towels or blankets to help maintain the correct temperature.

7 tips for maintaining the correct mash temperature

Getting to know your setup is an important part of learning to homebrew. Each time you brew, you should write down the temperature and volume of water added at each stage.

When I first started brewing, I mashed in the same pot that I boil the wort in. Although a good way to get started, I found it quite difficult to hit and maintain the correct mash temperature consistently.

I soon upgraded to using a modified picnic cooler. This has improved results considerably, and I seldom need to adjust the temperature mid mash. These are my top tips for single-step infusion mashing in a picnic cooler.

  • Select the right sized cooler. For maximum heat retention, the cooler should be full, with no air space at the top.
  • Pre-heat the cooler before adding the mash. Before I start heating the water for the mash, I fill the cooler with hot water from the tap and let it sit with the lid on. This preheats the cooler to almost the right temperature.
  • Heat the water to 75ºC and partly fill the cooler before adding the malted barley. This will allow the cooler to get up to temperature.
  • Add the malt and hot water a bit at a time, stirring slowly to ensure that no dough balls form.
  • Once all the malt and water are mixed in the cooler check the temperature and adjust if necessary. When you mixed in the malt, the mash will have cooled to below 70ºC.
  • Check the temperature of the mash every thirty minutes and be prepared to correct it if necessary. A digital thermometer has the advantage that you can check the temperature regularly without having to remove the lid from your mash tun or kettle.
  • Relax, even if your mash temperature is off by a couple of degrees, you’ll still end up with a nice tasting beer.

What to do if the mash temperature drops too low

A lower mash temperature can be easily fixed by adding a small amount of hot water from an electric kettle. Simply boil a litre of water and add to the mash until you reach the correct temperature. Make sure you note down the volume of water added and deduct it from the sparge water.

What to do if the mash temperature is too high

On the other hand, if your mash is too hot, you can add a handful of ice cubes or a jug of cold water until the mash cools to the correct temperature. Once again, you should adjust the amount of sparge water to compensate for the extra volume.