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Magic Numbers of The Mash

The mash is by far the scariest and most confusing part of the brew day for new brewers. When learning to brew, we are confronted with a multitude of temperature ranges and absolutes that we mustn’t stray from or else our beer will be ruined! This is then further complicated by the fact that the biggest homebrewing community in the world quotes all these ranges and absolutes in degrees F despite what the rest of the world thinks!

EINBREW 3V2P controller temperatures
Brown trace shows Mash Tun temperature during mash steps.

By understanding the science behind the mash we can start to decode those magic numbers and make more informed decisions about whether or not we need to worry about straying from the ranges quoted in recipes.


Despite how it might look, the mash is not magic. In fact, it isn’t even chemistry, it is biochemistry. This means that the whole process is controlled by a team of enzymes referred to colloquially as ‘the diastatic enzymes’. When someone says that a grain has a lot of ‘diastatic power’ they mean that it has a lot of these enzymes in it. This team of, basically 3, enzymes each play a role in converting the complex carbohydrates (starch) in malt into sugar that can be fermented by yeast (in this case maltose).


Each diastatic enzyme has a different optimal temperature and this is why we have so many guidelines about what temperature we should use for our mash. This can get very confusing and so here are some guidelines on what you might expect when mashing at various temperatures:

1. Too Cold (45C / 113F): At this temperature the mash is very thick and very hard to handle. At this temperature starch isn’t gelatinized and so basically nothing will happen. Starting here and raising the temperature, however, can help to break down certain proteins and release more of the diastatic enzymes. This can help to ultimately make a more fermentable wort. It is worth noting that doing this sort of mash is quite difficult for most low-end pumps to handle.

2. Too Hot (70+C / 158F): At this high temperature most of your enzymes will be lost. One of the diastatic enzymes, however, will survive. This is the enzyme responsible for making ‘dextrins’. These contribute to starting gravity but aren’t fermentable by yeast. A hot mash, therefore, can make a wort that will have a high finishing gravity with a lower-than-anticipated alcohol content.

3. Just right (64-67C / 147-153F)? In theory this is the real magic range. At this temperature the mash isn’t a gluey mess, the starch is gelatinised, there are enough enzymes alive and well in solution and they are able to work quickly. Straying from this range MIGHT have deleterious effects but it is worth noting that if the temperature goes below 64C (147F), the worst that will happen is that things will slow down. If you go a little above 67C (153F) you may lose some enzymes but realistically, not all of them will die at once, allowing you to get back into range quickly.

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