The mash is one of the least understood processes among brewers. Mashing is both a procedure and a scientific phenomenon – it’s possible to properly conduct a mash without any knowledge of chemistry. But the more you know the better your chances of squeezing every bit of sugary goodness out of your grain. To fully understand the mash a bit of background knowledge about malting is useful – check out my articles on malt and base malts for more information.
Grain kernels are filled with a very large branching carbohydrate called starch. Starch is essentially hundreds of glucose molecules all stuck together, and it functions as an energy reserve for plants. During malting, grain kernels are germinated so that they begin growing. This process activates amylase enzymes, which work to break down the starch stores into simple sugars to feed the growing plant. During fermentation, the yeast feed on sugars in the beer and convert them into ethanol and carbon dioxide. But yeast are not able to consume starch – it’s simply too big and they lack the enzymes needed to break it down. So to feed the yeast and get the fermentation products we desire, the starch in the malt needs to be broken down to the simple sugars they’re able to consume. Fortunately for brewers and beer consumers alike, amylase enzymes can be released from their cereal prison and harnessed to make beer. This process happens in the mash.
Enzymes are natural catalysts that speed up chemical reactions. In the case of amylase enzymes, they speed up the breakdown of carbohydrates like starch. Amylase enzymes have a particular shape that fits over the starch molecule and helps to cut off sugar molecules. The particular shape of the enzyme is very important for its function, and is affected by factors like temperature and acidity. There are three primary amylase enzymes that work in the mash; limit dextrinase, beta-amylase and alpha-amylase.
Limit dextrinase chops up the branches of the starch molecules into straight chains of glucose that can be broken down by the other amylase enzymes. Beta-amylase works systematically from the end of a glucose chain, chopping off two-glucose sugars called maltose as it goes along. Alpha amylase works along the glucose chains randomly, chopping the chains into smaller chunks that can then be broken down further by beta-amylase. These enzymes function most effectively in a temperature range of 60-70 degrees Celsius and a slightly acidic pH. Limit dextrinase and beta-amylase prefer the cooler end of the temperature range, being most effective from 60-65 degrees Celsius and a pH between 5-6. Alpha amylase functions well in the full 60-70 degrees Celsius temperature range and a slightly more acidic pH of 4-6.
For the mash to function properly, the malt needs to be crushed to release the starch and enzymes. The crushed malt is then mixed with water at the desired mash temperature. This frees the enzymes, and causes the starch molecules to absorb water and swell up. The hydrated starch is then able to broken down by the enzymes. To get the maximum conversion of starch to sugar, the environment should be optimal for the enzymes.
The actions of the different enzymes have different effects on the finished beer. Yeast only ferment simple sugars like maltose, so the action of mash enzymes determines how fermentable the wort will be. A lower temperature mash that favours beta-amylase will result in a highly fermentable wort. A more fermentable wort means that more of the sugar will be eaten by the yeast, and less will be left in the finished beer. This results in a beer with a higher alcohol content, but a thin watery body. A higher temperature mash that favours alpha-amylase and limit dextrinase will mean the beer contains more unfermentable sugars, so will have a thicker body and some residual sweetness. Targeting a mash temperature in the middle of the enzyme range and a pH of around 5 will produce a beer with a balance of alcohol content and residual sweetness. Mash temperatures can be manipulated to affect the characteristics of the final beer.
It takes approximately 60 minutes for the enzymes to convert the starch in the mash into sugars. Lower temperatures will cause the enzymes to operate more slowly, so it’s recommended to mash for 90 minutes if targeting a more fermentable wort. Starch conversion can be completed in as little as 30 minutes at the higher end of the temperature range, but it’s still recommend to allow the mash to rest for 60 minutes.
Multi-rest mashing is also possible. In this case the mash is held at different temperatures to favour different enzymes. A popular multi-rest schedule rests the mash at 62 degrees Celsius for 30 minutes and 70 degrees Celsius for 30 minutes to create a balanced final beer. Now that you understand the workings of the mash, try targeting different temperatures and see how the different enzymes affect your finished beer. You might be pleasantly surprised!