The first time I mashed my own grain, I was honestly surprised when wort started to flow from the mash tun’s ball valve. I understood that, yes, in theory, given enough time at the right temperature, enzymes would reduce starches in the malt to fermentable sugars. But the whole thing just seemed too…well…easy. Dare I say, magical, even?
Most of what happens when we brew beer takes place at the microscopic level, so it’s easy to forgive the writers of the 1516 Reinheitsgebot for neglecting to add yeast to the list (the first modern microscopes were at least 50–100 years away). How, then, could anyone even begin to fathom that enzymes, which are far too small for ordinary light microscopes to resolve, are responsible for the conversion of starch to sugar? For early brewers, it just sort of happened.
Fortunately, we know much more today and make substantially better beer than did sixteenth-century brewers. There are many, many enzymes at work in a typical mash, but for the vast majority of beers brewed by the vast majority of homebrewers, only two enzymes require much thought: alpha and beta amylase.
What we commonly refer to as the saccharification step in a single-temperature mash really involves two related types of activity, the nature of which is determined by these two enzymes. For the sake of simplicity, think of all starches as resembling a tree limb (specifically, think of them as deciduous tree branches in winter—this analogy has no use for leaves). Each branch of the limb consists of a long chain of sugars that are linked together. In fact, starch is nothing more than a complex string of sugar molecules. Here’s why we have to worry about two enzymes.
- Beta amylase, the low-temperature enzyme (130–150°F/54–66°C), can snip just one sugar molecule at a time from the free end of a branch, but it can’t work on areas where two branches meet. Given enough time, it can eat through a lot of starch, but it’s going to have trouble when it gets near those junctions.
- Alpha amylase, the high-temperature enzyme (150–160°F/66–71°C), works in a more random fashion and can split molecules at various locations, including the junction of two branches. Every time alpha splits one of those branching locations, it opens up new free ends for beta to do its thing.
In a traditional stepped mash schedule, the brewer first holds the mash for a period of time at a temperature favoring beta amylase (say, 140°F/60°C), then heats it to a temperature favoring alpha amylase (like 158°F/70°C) for another rest. This ensures that each enzyme has ample opportunity to work within its optimal range of activity.
With the widespread availability of well-modified malts, however, professional brewers and hobbyists alike have gravitated en masse toward a single temperature that offers both enzymes time to work simultaneously. That single temperature is usually between 146°F and 156°F (63°C and 69°C), which is near the upper end of beta amylase’s preferred range and near the lower end of alpha amylase’s.
Fortunately, enzymes don’t really work in an on-or-off digital fashion; they just get more sluggish when they’re not within their optimal temperatures. Certain temperatures are preferred over others, yes, but it’s not until you hit the denaturing temperature that you’ve essentially “killed” the enzyme. And the denaturing temperatures for beta and alpha amylase are about 160°F (71°C) and 170°F (77°C), respectively.
It is for this reason that mash protocols often include a so-called “mash-out” step at around 170°F (77°C). Pushing the mash to this temperature denatures the enzymes and locks in wort composition, ensuring that the wort you have before latuering is the same wort you’ll end up with at the beginning of the boil.
You don’t have to understand enzymes to make great beer. All you really need to know is that mash temperatures that favor beta amylase create more fermentable wort sugars than mash temperatures that favor alpha amylase. This is why you’ll often hear brewers speak about “mashing low” or “mashing high.” Target the low end for those Belgian styles that need a bone-dry finish and aim for the upper end for British styles that need a lot of residual body.