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The Right Temperature

Now here comes the science bit. These enzymes I’ve mentioned only work at certain temperatures, and, inconveniently, they all work at different ones.

We could get bogged down in glucanase and peptidases – all the “ases” – but all we need to know is that these two help keep the beer clear and improve retention of the foamy head. More important to us are the alpha and beta amylases that break down the starch. Think of the alpha as a maniac lumberjack with a chainsaw who is chopping down trees at random, while the beta is a madman with an axe splintering smaller pieces off the trees. The yeast can only consume the small bits, so alpha doesn’t give them much to work with because it chops all kinds of sizes. Beta, meanwhile, chops at the bases and makes lots of little fermentable bits. Beta turns most of the starch to sugar, but it can only reach so high, so a little bit gets missed.

The reason I’m over-investing in this metaphor is because this is where the mouthfeel and lots of the flavour is decided. Because the alpha enzymes like chainsawing at high temperatures (around 70ºC/158ºC) and the betas want to start chopping at cooler ones (around 62ºC/144ºF), the temperature you mash at is vital to the rest of the brew.

If you mash at the lower ranges of the beta zone, you’ll end up with a thinner, drier beer. That’s because the betas broke down most of the thick body-providing starch chains, turning them into sugar that was eaten up by the yeast.

If you mash at a higher temperature, you’ll get fuller-bodied, sweeter beer because the alphas didn’t break down all the chunky chains of starch into sugar, leaving it unfermentable.

Most beers are mashed right in between these two ranges. It gives you the sugar you need while not taking away all the body from the beer. When writing a recipe, this is taken as the standard that the brewer deviates from to tailor his mash to the beer in his head. It may be he is making a big imperial IPA and needs all the sugar he can get, so he’ll mash in low. Conversely, if he’s making a 3.8% session IPA, he’ll mash high to leave some body and unfermented sweetness to inject flavour.

As the temperature ranges are pretty small, accuracy is key – keeping control of the mash temperature, and nailing it at the start (known as the “strike temperature”), is vital to get it like Goldilocks wanted: just right.

The Right Acidity

The enzymes at work in the mash prefer a specific pH, so most brewers aim at between 5.2 and 5.5. That’s pretty much the Golden Rule unless you’re making a sour beer, and even then the drop in pH usually happens during fermentation even when you’re using acidulated malt.

Getting the pH of the mash right is a bit of a battle because the kind of malt you add changes it. Thankfully, most water supplies are slightly alkali and, if you’re lucky, nature can do the work for you because dark malts lower the pH. You can also tweak the mash using brewing salts, but this can have an effect on the flavour of the beer. German brewers—who have to stick to certain rules to adhere to that all-important marketing tool, the Reinheitsgebot—use a little acidulated malt to get the right pH.

The Right Time

You can mash for as long as you want. Usually it’s for around an hour, but for an imperial stout it could be several to convert all the starch. The longer you do it, the more sugar you will extract because the enzymes will have more time to work. A longer mash also allows brewers time to change the temperature of the mash – going through the beta temperatures up to the alpha to break down as much as possible. However, not all mash tuns are set up for this, so most brewers stick to one temperature.

The Right Gravity

Brewing is all about having a clear destination in mind, and in the mash that destination is the correct “original gravity.” This is a measurement of the sugar-to-water ratio in the sugary liquid that is now known as “wort”. Too high and the beer could be more alcoholic than intended, too low and it could be weaker. At the end of fermentation, the “final gravity” – or remaining sugar concentration – is measured and the difference between the two reveals the ABV (alcohol by volume) of the beer.

In homebrewing, the gravity is measured using a hydrometer, which is a long, absurdly thin glass tube that floats in the wort. The original gravity is indicated by how high it sits in the liquid. Ask any homebrewer how many times they have smashed their hydrometer and you will learn what most of them think of this particular piece of equipment. Only a little more robust is the refractometer, which is less accurate but has the advantage of making the brewer look like a pirate.

Getting the right gravity is a tricky little game played by brewers once the mash is over. The malt has been steeped, stirred and broken down to release its sugar, so now the brewer needs to collect it. This is done by opening up the bottom of the mash tun and pouring hot water (around 168ºF) in from the top. This water filters through the grain, collecting all the sugar before making its way into the next vessel, the kettle. This process is known as “sparging” or, when using a second vessel called a lauter tun, “lautering.”

As it goes through, the brewer takes a sample to measure. From that, he works out how much water he’ll need to get the right original gravity. This happens several times during the so-called “run off” because the first few litres of wort are usually more concentrated than the last few. Lovely as water is, the last thing he wants to do is add too much and end up diluting the beer.