It’s easy to take highly modified malt for granted. Today, it’s challenging to find one that’s not; even most European Pilsner malts are fairly well modified. For homebrewers, that means that a single-step infusion mash works great most of the time.
Multi-step mashing may seem like a historical curiosity, but it’s good to understand the intent because there are still some useful ideas. Stopping points during the mash process were designed to improve the quality of the beer based on the available malts, but they can also come in handy when you’re using unmalted grains, such as wheat, rye, or oats, or when you want to study traditional technique without the modern shortcuts.
Let’s look at the rest points and see what they’re all about.
Acid Rest / Doughing In
Czech brewers used an acid rest to deal with their combination of pure low-mineral content water and recipes limited to pale malts. Without this step, their mash pH would fall higher than 5.0–5.5, which would inhibit mash enzymes as well as yeast activity during fermentation. Letting the mash sit for an extended time around 104°F (40°C) allows the phytase enzyme present in the grain to break down an organic phosphate (phytin) to yield a mild acid.
Water-chemistry adjustment is a much more efficient way to hit that target pH, but there are still benefits to doughing in at 104–113°F (40–45°C). A 20-minute rest ensures that enzymes are well distributed within the mash and that the grain is wetted, providing the enzymes access to the starch.
In addition, this is a good temperature for breaking down beta glucans, which can gum up the mash, leading to a stuck run-off. They can also cause haze in the finished beer. If your recipe includes a moderate amount of unmalted grains or under-modified malts, it’s worthwhile to include this rest, especially if you have had problems with your sparge.
Protein Rest
Malt proteins offer benefits and drawbacks. The right combination contributes to body and head retention, but long-chain proteins can also lead to cloudy beer. When most malts were less well-modified, a 20- to 30-minute protein rest between 120–130°F (49–54°C) would hit that sweet spot and break down large proteins. There are a couple of enzymes in play. Protease cuts the longer chains into medium-sized chunks, which will support the body and head retention. Peptidase, on the other hand, breaks down the medium-sized chains into smaller bits that the yeast can use during fermentation.
The catch is that recipes primarily based on fully modified malt don’t have as much protein to contribute, so this rest will actually result in thinner body and lousy head retention. A good rule of thumb is that you should skip the protein rest unless you’re using a moderate amount of unmalted grain or a fair amount of less well-modified malt, especially if you’re getting boutique malt with a higher protein percentage (but these days, most Pilsner malts wouldn’t even require it).
Saccharification Rest
If you’ve been doing single-step infusion mashes, this rest is one you’re already familiar with. This is where the starch gets converted into sugars. Even if you skip the other rests, you might want to consider splitting your single step into two steps. To understand why, we need to examine the enzymes working during saccharification.
Alpha amylase cuts up starch chains at random locations, which creates larger, unfermentable sugars. Because it can slice anywhere in the chain, alpha amylase can chew through the starches relatively quickly. By contrast, beta amylase behaves more slowly and methodically; it splits off highly fermentable maltose molecules from the ends of the chain.
The amylase enzymes have different optimal temperature ranges, but there isn’t a sudden drop off for either one. Beta amylase works best between 130–150°F (54–66°C). Alpha amylase prefers a warmer 154–162°F (68–72°C), but it will still perform at cooler temperatures. This is important because breaking up those long-chain starches gives the beta amylase more ends to work on.
Single-step mashes effectively set a relative balance between the two enzymes. Mashing at 148°F (64°C) favors beta amylase, creating a drier flavor and more alcohol, while a mash at 155°F (68°C) pushes the balance to alpha amylase and a sweeter, more full-bodied beer. You can tweak that balance further by hitting each of the optimal ranges but adjusting the time spent in each. A 40-minute rest at 145°F (63°C) will give the beta amylase time to process much of the starch, but some unconverted starch will remain. Following up with a 10- to 20-minute conversion rest at 158°F (70°C) will let the alpha amylase convert the rest into dextrins. Flip the times—20 minutes at 145°F (63°C) and 30–40 minutes at 158°F (70°C)—and you’ll get a richer malt profile along with the sweetness and body.
Mashout
Some brewers omit the mashout step of raising the mash temperature to 168–170°F (76–77°C). That higher temperature serves to denature the amylase enzymes and shut down saccharification. Without a mashout, the enzymes may continue working during the sparge. That may lead to a loss of body and sweetness. In addition, the mashout can prevent stuck sparges by making the mash liquid a bit thinner (think of how temperature affects oil viscosity). This is even more important with huskless grains such as oats, wheat, and rye.
A journey begins with a single step, but you can learn a lot with a couple more. Give multi-step mashing a try.