Understanding Mash Profiles

Key points

  • Use a longer β-amylase rest at 64C or 148F for a drier finish, but less efficiency 
  • Use a longer α-amylase rest at 70C or 156F for a sweeter finish and more efficiency 
  • Combining the two rests will give you more efficiency and cut down on the sweetness, but it will still be sweeter than a  β-amylase rest alone unless you extend your mash time or add enzymes.

Some newer brewers who have entered competitions may have had judge feedback sheets that say something to the effect of “mash higher” or “mash lower” for increased or decreased sweetness or body. Here, we’re going to dissect what that means and how it works so that you can choose a mash profile to create what you ultimately want.

To start, malt choice matters a great deal and there’s only so much that you can do in the brewhouse. Making a porter with 100% brown malt will make something undrinkable nowadays, no matter what you do to it in the mash tun. It’s why long aging times were required, to allow Brettanomyces to break down many of the dextrins that were unable to be broken down in the brewhouse. That, however, is the subject for a different article and so for this article, we’re going to assume you’re using a basic pale 2-row malt (you can read more about basic 2-row here.)

In barley, there are two main types of starch, amylose and amylopectin, and, for the purposes of this article, two enzymes that will break them down, α-amylase and β-amylase.

Amylose is a long chain of glucose units in a row.

It represents about 30% of the total starch in the barley kernel. It is easy for our first enzyme to digest, β-amylase. β-amylase is most active at 64°C or 148°F and will start to degrade at higher temperatures. Even so, it will start to degrade after 60 minutes at its optimum temperature. When enzymes degrade, they will still remain active, but you will lose many of them and they will become less effective as time goes on. β-amylase will methodically snip off maltose units from one end of the amylose chain until it is gone.

The second starch, which represents 70% of the total starch in barley, is amylopectin. This one is shaped more like a tree branch.

There are plenty of ends that β-amylase can start snipping at, but once it reaches the trunk, it can’t go any further, leaving a bunch of residual starches.

Thankfully, our second enzyme, α-amylase is active, though much slower at these temperatures. It will hack away at big starches randomly, exposing more ends for β-amylase to nip away at. Raising the temperature to 70°C or 158°F will make α-amylase much more active, but will denature β-amylase very quickly.

So what does this mean for all of us and how can we use this to our advantage? First, it helps to distinguish between starches, dextrins, fermentable and unfermentable sugars.

Starches: Tasteless, long chain sugars. Will turn black on an iodine test

Dextrins: Tasteless, shorter chain sugars. Will not turn black on an iodine test

Unfermentable sugars: three to four unit sugars that taste sweet, but aren’t useable by yeast

Fermentable sugars: two to three unit sugars that taste sweet, but will be consumed by yeast


So we’re going to pretend that this strip represents all of the starch in a barley kernel. It’s never 100% starch because some of it has broken down during the malting process, but for simplicity’s sake, we’re going to pretend it’s 100% starch. Starch is red.

If we go through a proper mashing procedure, in theory, no starch should be left and an iodine test should confirm that. This means that you will have a spectrum of sugars, including dextrins (no flavour), unfermentable sugars (sweet) and ferementable sugars that will be consumed by the yeast.

If you opt for a β-amylase rest only (we’re ignoring protein rests for the sake of this article) your sugar profile will look like this:

Yellow represents fermentable sugars and blue is dextrins. As you can see, there are plenty of fermentable sugars, some dextrins, but no unfermentable sugars and so the beer will taste dry.

If we do an α-amylase rest only, your sugar profile will look like this.


Light blue represents unfermentable sugars. There are fewer fermentable sugars overall, but far fewer dextrins. Compared to a β-amylase rest, this rest will give you higher efficiency.

If you opt for a multi-temperature rest, your starch profile will look like this:


                You end up with fewer dextrins, but also some sweetness as the β-amylase is mostly denatured by the time you get to this point. If you want the efficiency, but still want to eliminate residual sweetness, you can leave the α-amylase rest for quite a bit longer, or add powdered α-amylase to your fermenter. One macro lager in particular leaves their mash for 4 hours as well as adding thermostable enzymes!

Sample profiles:

  • Light, but inefficient - 64C (148F) for 75 minutes
  • Sweet and efficient - 70C (156F) for 60 minutes
  • Medium sweetness and very efficient - 64C (148F) for 60 minutes, 70C (156F) for 20 minutes