All Grain Brewing Explained: Part One – The Mash

So in a previous post I gave a brief description of the all grain brewing process. This was amazingly simplified and suited me as all I wanted was to take a recipe, follow it blindly and end up with a finished product. Which is fine, but I have an insatiable curiosity and I wanted to know more about the process.

Cue much internet searching, forum visiting, book buying and note taking. What I’ve learned from this is that the art of homebrewing is more than follow the instructions and hope for the best. The amount of control I have is astounding and I truly didn’t realise that. So I wanted to share this info with you, maybe you’re like me and have been home brewing for a while. Maybe you’re just interested in the science behind it. Maybe you just want to read what I’ve written and then mock me for getting it all wrong. But in any case I would like to present to you Part One of a (hopefully) ongoing series on brewing your own beer starting with –

THE MASH (I wanted to add MONSTER between THE and MASH, but I think that it would be irrelevant and not make sense to anyone but me)

So what is it? What does it do?

Well it is the first step in creating the sweet sweet liquor that will become the beer.

Although what it actually is, is malted barley porridge. Yup, that’s it. Crushed malted barley, maybe a few other types of adjunct thrown in. But mostly malt barley. And hot water. mix it all up, leave to stand for an hour to an hour and a half, then drain and rinse. What you collect is a sticky sugary liquid, called the wort.

It’s a funny word, wort, it’s one of those words where you say it over and over again and think to yourself, “That’s not right”. It’s even pronounced differently – wert. If you’re interested have a look at the Wiktionary entry, I’ve copied the entry below if you don’t want to click the link:

Wort – Liquid extract from the ground malt and grain soaked in hot water, the mash, as one of the steps in making beer.

From Middle English wort, worte, from Old English wyrt, wyrte (brewing wort, new beer, spice), from Proto-Germanic *wurtijō (spice), from Proto-Indo-European *wr̥h₂d (sprout, root). Cognate with Dutch wort (wort), German Würze (wort, seasoning, spice), Danish urt (beer wort), Swedish vört (beer wort).

Anyway back to it..

Why does the starchy grain transform, as if by magic, to sugary grain? To explain this I need to describe what the malting process is and what it does to the grain.

The Malting Process

The barley grains are delivered to the malt house, where the grains are submerged in water, they are then raised out in a drying phase, which is repeated several times. This process is to increase the moisture levels and prompt germination.

The grains are then cast out into beds to germinate. This germination process prompts the development of the required enzymes needed to convert the starchy grain into sugar. The beds are turned regularly to dissipate the heat generated from the germination process.

The grain is then kilned to dry it out and stop germination. It is then processed to remove the rootlets. This is called deculming.

Photo taken by Peter Schill – Self-photographed, CC BY-SA 2.0 de, Link

This whole ‘Malting’ process does the following –

  • Converts the hard insoluble starch into a soluble one. Malted barley is 80% soluble
  • Develops the enzymes needed for conversion
  • Develops Maltose and Dextrins in the grain
What the pH?

One factor that can affect the mash is the pH of the water. From school you may remember that pH is the scale used to define whether something is acid or alkaline. the neutral point is 7.0, which most of the water we use sits at, but it could be either side of that. If like me you went to school a long time ago and can’t remember the pH scale here is a handy info-graphic from the good old BBC

The optimum for proteolytic enzyme activity is in the region of pH 4.2 – 5.3 and the optimum for diastatic enzyme activity is pH 5.2 – 5.8.  We as homebrewers would want to make the mash sit at pH 5.2 (at room temperature, the pH value slides 0.2 – 0.3 at the mash temperatures). This is the best of both worlds for the enzymes to work at. If you look at the above chart it becomes apparent that the water needs to be acidic (the numbers are less than pH 7). So we have to adjust the pH to suit. I can hear you all saying now, “How are we to do that? We’re not chemists, we just want to brew beer!”

To grossly simplify things, because a lot can depend on water profiles, but when you mix the grain with the water it brings the pH to around 5.2. Sort of. Kinda. Well I did say it was an over simplification. I’ll cover off water chemistry in another post.

It’s all magic!

So why does adding hot water to the grain convert starch to sugar? Because of the enzymes created during the malting process. Well two types in particular –

  • Proteolytic enzymes (these degrade proteins)
  • Diastatic enzymes (these degrade starches)
So we know that putting the grain in hot water activates these enzymes, but how hot does the water need to be?
The protein rest

For the proteolytic enzymes to start breaking down the nitrogen based proteins into good wholesome nutrients for the yeast to munch on during fermentation, the water needs to be at between 45 – 50 °C. These nutrients are important in establishing how well the yeast attenuates (attenuation – the process of fermentation performed by the yeast to produce alcohol and CO2). Between 50 – 60 °C different proteolytic enzymes become activated and start breaking down the proteins to enable a frothy head when the beer is poured, and also helps the beer to clear down.

This temperature step is called the protein rest. If using a modern well modified malt this step isn’t necessary.

Diastatic disco.

The real workhorse enzymes are the diastatic ones. These change the starch into fermentable sugars and un-fermentable dextrins.

There are two diastatic enzymes that do all the hard work

  • Alpha-amylase
  • Beta-amylase

The fermentable sugars are all glucose molecules. Imagine them as a length of chain, all the links joined together in a large unwieldy jumble. Have you ever had to carry a load of chain? It’s heavy and difficult to manipulate. So the alpha-amylase takes its cutting torch and starts to cut the chain into smaller and smaller chunks. Then its buddy, beta-amylase starts to work breaking these small chunks down even further, down into smaller pieces of one, two and three links in length. I like to think of these two enzymes as junk yard workers, turning the large pieces of scrap into nice useful smaller pieces. These smaller pieces consist of:

  • one link = glucose
  • two links = maltose
  • three links = maltriose

Then there is a four link chain, this is a dextrin. This is still a sugar but the yeast can’t eat these, so they remain, adding body to the beer and gives it that nice smooth mouth feel.

Nature is amazing.

Heat it up!

The temperatures needed for our two friends, alpha and beta, to work at their best are different though:

  • Alpha-amylase works best at between 65 – 67°C, but stops working after 2 hours at 67°C.
  • Beta-amylase works best at between 52 – 62°C, but stops working within 40 – 60 minutes at 65°C.


Both work very well together (usually) at 63 – 70°C.

What does this mean for the homebrewer? Well do you want a beer with lots of body but not as alcoholic? Mash at the higher range of 67 – 70°C. Want a beer that ferments dry and is strong at the expense of body? Mash in the lower range of 63 – 65°C. You will find the happy median at 66°C.

So we’ve established the best temperature, but for how long?

It depends…

There are lots of variables here:

  • Temperatures
  • Amount of enzymes activated
  • Amount of starch available to be converted

At higher temperatures, say 70°C, you could mash for a short time of 15 – 20 minutes. But there would be a lot of unfermentables in there, which wouldn’t give much sugar for the yeast to utilise.

At lower temperatures, around 63°C, the mash would be 90 minutes+. This would give a load of sugars, but would lead to a strong thin watery beer.

(This is all based on a standard mash with no more than a quarter of the grist being none malt adjuncts)

So if you mash at 66°C for 60 – 70 minutes, this gives a balanced wort. I use this temperature/time combo successfully, but your mileage may vary. At the end of the day these figures give you the base to design a beer that you want or the beer style you want to achieve.


So you’ve mashed and held your temperatures for the desired time. Our friends the enzymes have used their magic to convert the starch to sugar and the wort is ready to be collected. It’s time to sparge. There are a number of different ways to do this, and the forums are full of different views on how this should be done and the reasons why. I use a method called batch sparging. The other way of doing this is fly sparging. What are the differences? Well, you’ll have to wait until the next post, as part two is all about – The Sparge.


Here’s an interesting thing, you can use potatoes as a source of starch. Potato beer! You want to go with the floury type of potato, such as King Edward or Maris Piper rather than the waxy types. The good thing is the starch is converted to flavourless sugars, which means that you wouldn’t get mashed potato flavour beer!

There is a bit of preparation, as the potatoes need to be peeled, chopped into 2.5cm cubes, then boiled for around 15 minutes and then mashed (not added to the mash, but crushed) once this is done add to the grist to be mashed. I think this would be handy if you were looking to do a batch of beer but didn’t have quite enough pale malt and the homebrew shop is closed or far away.

Want to try it? Here’s how to work out how many spuds you need –

Potatoes have 22% dry weight, of that 75% is starch. The potential extract is 7.6 points per 450 grams per 4.4 litres (in old money that’s 7.6 points per pound per gallon)

So 2.2 kg of potatoes with a dry weight of 0.5 kg = equivalent potential extract as 0.45 kg of 2-row pale malt.

Thanks for reading, please leave comments. and if you have questions feel free to ask and I will do my best to answer them.

I would like to thank the r/Homebrewing community for pointing out and helping to clarify a few things in this post. Thanks to – flappymcflappypants, Fapinthepark, dillsnick, seanbikes, carlgauss, osorojotx, moldiemom


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