Mashing: Get To Know Your Enzymes

Mashing is a fundamental part of all grain brewing and if you are anything like me, the thought of making the leap from extract brewing to all grain mashing was an intimidating one. At the outset it brings with it a number of anxieties that the producer of the malt extract has borne for you in the production of ready fermentable extract.

Mashing is a complex procedure at the biochemical level with any number of molecular processes that must be provided a suitable environment to work effectively. Thankfully, providing a suitable environment is relatively simple using home brew equipment and in this article I hope to explain some of the biochemical reactions that are so important for effective mashing.

Our Friends the Enzymes

Enzymes are essential in making the sweet wort which yeast metabolise to produce ethanol during fermentation, but what exactly is an enzyme?

Enzymes are a form of molecular machinery that are exquisitely designed to carry out specific chemical reactions. They are proteins that harbour an ‘active site’ which has great affinity for a particular molecule and vastly increase the speed of a specific chemical reaction that involves the molecule. They often require specific conditions at which they work most effectively and this is an important factor when mashing. So, which enzymes are important to the brewer?

1. Phytase

This enzyme is responsible for producing phytic acid from malt constituents. Phytic acid lowers the pH of the mash and helps the brewer to reach the required pH for the mash to work effectively

2. Carboxypeptidase

OK, this sounds like a complicated one but it has a simple enough role. This enzyme releases amino acids from protein in the malt. Amino Acids are an important source of nitrogen for yeast, without which fermentation will not go well.

3. The Amylases

The amylases are perhaps the enzymes that all grain brewers are most familiar with and the demands of the amylases are what concerned me most when I considered doing an all grain mash. I worried about how I would keep these finicky enzymes happy so they would convert the starch in my mash to lovely sweet wort. I mean, isn’t there all kinds of pH and temperatures to worry about? It turns out it’s not that hard to do, as long as certain parameters are met.

First up is β amylase.

As I said earlier, the amylases break down starch. Starch is a huge molecule composed of a great many glucose units, while the most common sugar in sweet wort is maltose, so something has to occur in the mash for this transformation to occur. Maltose consists of two glucose units stuck together. β amylase’s role in life is to cleave maltose units from starch molecules which yeast then make short work of during fermentation.

Next up is α amylase

This enzyme also breaks down large starch molecules in the mash but it does so in a more haphazard way. This enzyme randomly cleaves starch producing small chains of glucose units that β amylase can further break down into maltose units. α amylase is referred to as the ‘liquefying’ enzyme because it can rapidly breakdown very large starch molecules.

With respect to the mashing conditions, the enzymes we are trying to keep most content and therefore productive are the amylases. Below is a table outlining the conditions that these enzymes like to work in.

We now have some idea of the conditions we need to meet to carry out an effective mash. But how do alterations in these conditions affect the quality and character of our beer?

Mash pH

While the malt itself has the action of the enzyme phytase to lower the pH and meet the pH value that the amylases like to work in, the work of this enzyme can be undone if the water used for mashing is too alkaline. This problem will occur if the brewing water has high carbonate levels because the carbonate will neutralise the acidity produced by the enzyme. Therefore appropriate water for the malt bill is essential.

Mash Temperature

Mashing temperature is a factor that brewers have a good degree of control over and it offers us a means to vary the character of our beer. If we look at the table listing the temperature optima for the amylases we can see that by choosing different mash rest temperatures we can favour the action of either α or β amylase, but how will this affect our beer?

If, for example, we wanted to brew a full bodied porter, we need to favour the action of α amylase because it will produce long chain glucose molecules (dextrins) that provide the full mouth feel appropriate for this style of beer. For maximum α amylase activity we should mash at around 68 ºC as this temperature is near the inactivation temperature and beyond the temperature optima of β amylase, therefore less of the dextrin produced by α amylase will be broken down to maltose. Remember, the inactivation and optimal temperatures are ranges, so there will be some activity at the upper and lower limits of these ranges.

If on the other hand we’re after a lighter bodied ale we could mash at a temperature that favours both of the amylases; say 66 ºC, because starch will be broken down by both of the enzymes and further to this the dextrins produced will be cleaved to maltose units which will be fully fermented by the yeast leaving less body in the beer.

Fermentability

A consideration that must be taken when choosing mash rest temperature is the degree of fermentability of the resulting wort. In our example of the porter earlier we must take into account that yeast are unable to ferment dextrins and make certain that there is sufficient β amylase activity to provide enough maltose for fermentation but not so much as to remove all dextrins from the wort. We can do this by ensuring the mash temperature does not exceed the upper range of the deactivation temperature for β amylase i.e. 70ºC

Conclusion

The best way to get a feel for the effect of mash temperature on beer character is to vary it within a set recipe and note the changes that occur in the beer. Hopefully I've shown that both the pH and temperature ranges that malt enzymes will work at are wider than we first might think and that good beer can be produced even if we have trouble reaching optimal conditions.

Happy Mashing!