It’s often been said that there are as many ways to brew beer as there are brewers. In fact, I don’t think that I know any two brewers who brew in exactly the same way.
Some of the differences in brewing technique are pretty subtle, and others are so fundamental that they can be classed as entirely different techniques or styles of brewing.
One of the most basic differences is how brewers choose to mash. The mashing technique can be divided into two distinct methods; infusion mashing and step mashing.
This post looks at what a mash rest is, what each type of rest is used for, and whether step mashing is even necessary.
What is mashing in home brewing?
Before we go into the details of step mashing, let’s start by defining what mashing is.
Mashing is the first stage of all-grain brewing when the brewer mixes the malted grains and other adjuncts with hot water forming a porridge-like mixture called the mash.
During mashing, the starch in malted grains is dissolved, allowing enzymes to break it down into sugar. Later in the brewing process, yeast converts the sugar into alcohol.
In addition to starch, the malted grains used to brew beer also contain protein and beta-glucans. During the mashing process, protein becomes dissolved in the wort, whereas beta-glucans can gum up the grains, preventing the starch from being extracted.
Dissolved proteins make beer cloudy or hazy and, depending on the style of beer being brewed, brewers usually try to reduce the amount of protein in their beer.
What is a mash rest?
Over the centuries, brewers have developed three different methods of mashing:
- Infusion mashing
- Step mashing and
- Decoction mashing
Infusing mashing (or single rest infusion mashing) is commonly used for brewing ales. In the infusion mashing process, the mash is held at a temperature between 63 and 70ºC (145 – 158ºF) for approximately one hour so that enzymes can convert starch from the grain into sugar. After this, the mash is recirculated and then rinsed to extract as much sugar as possible from the grain.
Step mashing is commonly used for brewing lagers, especially when using partially modified German malts.
In step mashing, the mash is held at a series of pre-defined temperature rests. The idea behind step mashing is that each of the different enzymes present in the wort works best at a specific temperature.
By maintaining the mash at a series of different temperatures, the brewer ensures that each enzyme can fully perform its task.
Decoction mashing is a traditional method of step mashing which was developed by German brewers. In the past, it wasn’t practical to heat the entire mash to a series of carefully controlled temperatures. Instead, brewers used to take a portion of the mash and boil it before returning it to the main mash to heat it to the desired temperature.
Temperature rests used for step mashing
The most common temperature rests used for step mashing are:
Let’s take a quick look at what happens at each of these temperature steps:
What is an acid rest?
Acid mash rest (aka beta-glucanase rest) is the first temperature rest used in step mashing. The mash is held at a temperature in the range of 35-45°C (95-113°F), allowing the enzyme phytase to release phytic acid, which makes the mash slightly acidic.
More importantly, at this temperature, beta-glucanase can break down beta-glucans which might otherwise gum up the mash, preventing starch from being released during the saccharification rest.
What is a protein mash rest?
The protein rest is a stage in the brewing process when the mash is held at a temperature of between 45 and 55ºC (113-131°F) for between ten and twenty minutes. This allows enzymes present in the grain (peptidase and protease) to break down and digest proteins which would otherwise make the finished beer hazy.
What is a saccharification mash rest?
The saccharification rest is when alpha and beta-amylase converts starch into sugars. Conversion takes place between 61 and 71ºC (142-162°F). More long-chain sugars are extracted at the higher end of the temperature range, creating a fuller-bodied beer. Mash temperatures at the lower end of this range extract more fermentable sugars, resulting in stronger beers.
Single rest infusion mashing employs a single saccharification rest that usually lasts around an hour.
The saccharification rest can be divided into two steps; the alpha-amylase rest and the beta-amylase rest.
What is a beta-amylase mash rest’
The beta-amylase rest is when the mash is held at a temperature between 60 and 65ºC (140–145°F). Beta-amylase breaks down starch molecules into maltose at this temperature, a fermentable sugar used by yeast to create alcohol.
What is an alpha-amylase mash rest?
During the alpha-amylase rest, between 66 and 67°C (150–152°F), alpha-amylase turns starch molecules into non-fermentable sugars which add sweetness and body to the finished beer.
Infusion mashing versus step mashing, which is best?
At this point, you might ask yourself why most homebrewers, and many commercial brewers, decide not to step mash. From everything that we’ve discussed so far in this post, step mashing must be better than infusing mashing, right?
Well, no, not exactly. Towards the beginning of this post, I said that mashing is the first stage in the all-grain brewing process. In fact, the first step in the brewing process takes place before the malted barley is delivered to your local homebrew shop.
Malting is the process of germinating the barley grains by soaking them in water and then heating them in the kiln to dry them and prevent them from growing any further.
The malting process releases enzymes that convert starch and proteins inside the grains into sugars and amino acids.
In the past, malting simply started the conversion of starch and proteins in the grain. Most of the enzyme activity needed to break down proteins and convert starch into sugar took place during mashing. Because of this, step mashing was traditionally the most commonly used method.
Nowadays, modern equipment and techniques allow malt manufacturers to convert a larger percentage of the barley’s starch and proteins into sugars and amino acids. This means that, in most cases, the acidification and protein rests are no longer necessary.
Whether or not you need to step mash depends mainly on the type of malt being used.
If you are using a modern fully-modified malt, then step mashing isn’t necessary. When using fully-modified malts, a protein mash rest may cause too-much of the dissolved protein to be broken down, causing watery beer with poor head retention.
Even though modern malt houses can produce fully-modified malt, some grain manufacturers decide not to. Many of the German malts used for brewing lagers and NEIPAs are only partly-modified and benefit from step mashing.