The importance of the enzymes present in malt cannot be understated. All the important biochemical reactions that occur in the mash tun rely on the enzymes that are present in malt. However, there is a complex array of enzymes that naturally occur in malt that all perform slightly different functions. To simplify things we can roughly divide the main enzymes in malt into 3 groups based on their functional properties. Thus the enzymes in malt can be grouped as detailed below:
- Protein degrading enzymes
- Starch degrading enzymes
- Cell wall degrading enzymes
All three groups are extremely important but if the maltster has done their job properly it is the starch degrading enzymes that we are most interested in. This is because the ultimate aim for us as home brewers is to effectively and efficiently convert the starchy endosperm into fermentable sugars.
The two main starch degrading enzymes that have the most impact during mashing are alpha and beta amylase. There are other starch degrading enzymes present in malt such as limit dextrinase and alpha glucosidase but their impact during mashing is relatively limited. Therefore for the purpose of this article we will focus our attention on the alpha and beta amylases.
If we look at what it is that we are trying to achieve during mashing it becomes clear why the amylases are so important. Yeast can be a fussy microbe and no more so when it comes to the sugars that it likes to ferment. Yeast, like most living organisms, is happier when things are simple and the simpler the sugars the better. When I talk about simple sugars I mean glucose, maltose, and maltotriose. Glucose is one of the simplest sugars that occurs in nature. It consists of a hexose ring structure and so is often referred to as a hexose sugar. Maltose and maltotriose are formed from glucose units joined together. Maltose is composed of two glucose molecules joined together and maltotriose is made up of three glucose molecules joined together. Yeast loves these types of sugars because they are easier to absorb and metabolise than bigger carbohydrates such as dextrins and starch. Therefore, to keep our yeast happy, one of the key aims of mashing is to break starch down into simple sugars that the yeast can ferment.
Starch itself is a highly complex carbohydrate composed of glucose molecules linked together to form one of two main structures. These two structures are a simple long chain molecule known as amylase and a more complex branched version called amylopectin. It is the role of the alpha and beta amylase to attack these two large carbohydrates and break them down. However, the way that they do this is significantly different. The enzyme beta amylase is very specific in its mode of action in that it will sit at the end of the carbohydrate chain and break it down into maltose. Whereas alpha amylase is a lot less specific in its mode of action as it moves along the chain and randomly breaks it down into smaller dextrins and straight chain carbohydrates. Neither alpha nor beta amylase will act on areas of the starch molecule where it branches which gives rise to the presence of larger unfermentable dextrins in the finished beer. These unfermentable dextrins are usually not a problem as they contribute body to beer but in some cases they can give rise to an unsightly haze.
Alpha and beta amylase are both critical enzymes in mashing but it is beta amylase that defines the fermentability of wort because it releases maltose from starch. Furthermore both alpha and beta amylase, because they are enzymes, are sensitive to pH and temperature i.e. there is an optimum temperature and pH at which they operate most efficiently. More importantly they both vary in their response to these two parameters. Therefore it is possible to dramatically alter the fermentability of wort and therefore the beer that you will brew by changing the temperature or pH of your mash. The table below details the pH and temperature optima for alpha and beta amylase.
|Alpha Amylase||Beta Amylase|
|Product of attack||Mainly unfermentable dextrins, few sugars||Maltose|
As you can see from the table if you are looking to increase the fermentability of your wort then you need to aim at a lower mashing temperature to favour the action of beta amylase. However, if you want wort that is less fermentable, which will give you a beer that is lower in alcohol, but with more body then a higher mashing temperature should be aimed for.
This is illustrated in the table below. As the table shows the maltose content elevated in wort that has been mashed at the lower temperature of 62ºC. This results in a wort that is more fermentable. Conversely as the mash temperature is increased so the maltose content decreases. It is also clear to see why many of us mash at 65ºC as this temperature is a good compromise option allowing both enzymes to function, although neither will function optimally.
Mashing is an important stage of the home brewing process and getting the temperature right is essential to enable us to produce the beers that we want to drink. I hope that after reading this article you are better equipped to build a mashing regime to enable you to create great tasting home brewed beer.
The next question that needs to be resolved is how do you ensure that you hit the correct mashing temperature. By calculating the strike temperature you should be able to hit the correct mashing temperature time after time. To find out what we mean by the strike temperature and how to calculate it read our article on how to calculate the mashing strike temperature.