Mashing is the process a brewer uses to convert the starches in grains into fermentable and unfermentable sugars. This is done with the help of enzymes which are already present in the grains themselves. There are different enzymes which are activiated at different temperatures, and which in turn have a different effect on the final product. The job of the all-grain brewer is to decide which enzymes should be activated for the specific type of beer being made, then to step the mash through a series of 1 or more timed temperature rests in order to activate in turn the desired enzymes, thus yeilding the desired effect on the final wort produced.

It is very important to note that there isn't a single mashing process, as such. There are actually a number of different methods used by homebrewers and commercial breweries alike to convert their starches into sugars. The various mashing processes can be broken down into 2 main categories :

• infusion mashing
• decoction mashing

Both methods begin with a pre-measured amount of grain being infused with a specific volume of strike water at a pre-determined temperature. After this initial infusion of strike water, depending upon the enzymes that are to be activated, the mash is stepped through its series of temperature rests. It is the method used to reach these rests which distinguishes the mashing methods.

Temperature Rests

Regardless of the method used to mash the grains - either infusion or decoction - the homebrewer will step the mash through a series of temperature rests, where the mash is held at a specific temperature in order to activate certain enzymes. The most common rests used, and the enzymes they are designed to activate, are listed in the following table :

* Protease is actually a general term for a number of enzymes which break down protein, it is not the name of a single enzyme.
* There is also a so-called "Acid Rest", used to lower the pH of the mash, but it is rarely employed these days, as the same results can be achieved with brewing salts

In short, the Protein Rest is used primarily when using a large amount of non-fully-modified malts. It activates enzymes which break down certain proteins in the malt into amino acids which in turn provide vital nutrients for the yeast. It also breaks down other proteins which cause haziness, thus allowing for the production of a clearer beer. These are both less of a concern with fully-modified malts, so many brewers skip the protein rest when using them. Care must be taken if a protein rest is employed, however, because it is these proteins which also provide the beer with a good frothy head. So if you remain too long at certain temperatures within the range of protein rests, you could experience negative effects on the final products in this regard. When beginning all-grain brewing, for the sake of simplicity it is advisable to use the fully-modified malts and skip the protein rest. In fact, it's pretty difficult to find malts these days which are not fully modified. Once the brewer becomes comfortable with the mashing process, this step can be added if desired. For one thing, some amount of chill haze can be eliminated by using the protein rest in the upper limit of the given temperature range.

The first conversion rest (Beta Amylase) is used to convert starches to fermentable sugars, while the second one (Alpha Amylase) is used to convert them to unfermentable sugars, which give more body to the beer. Often these two rests are combined into a single rest between 65 C (149 F) and 68 C (155 F), with a lower temperature (and longer rest) yeilding a more fermentable wort and subsequently a lighter bodied beer, and a higher temperature (and shorter rest) yeilding a less fermentable wort and fuller bodied beer. This combined rest is usually between 60 and 90 minutes long, depending upon the exact temperature.

Infusion Mashing

The most common method homebrewers use for mashing grains is the infusion mash. With this method, the homebrewer reaches the various rests either with the addition to the mash of a specific amount of boiling water, or with the addition of heat to the mash tun. The brewer usually chooses a method based on the the type of mash tun they use.

When using a pot on the stovetop, the increments are acheived with careful bursts of heat from the stove element. All the while the mash is stirred regularly, and the temperature carefully monitored with an accurate thermometer. When the desired temperature is reached, the rest is begun. The same effect can be had with cooler mash tuns by starting out with a thicker mash (less water) and carefully adding specific amounts of boiling water to the mash, while stirring and carefully monitoring the temperature. Many people use one of the various brewing computer programs to calculate exactly how much boiling water to add.

Decoction Mashing

Decoction mashing was the method used universally, before the days when temperatures could be accurately measured, and is still the preferred method in commercial breweries in Germany. Here, instead of adding heat directly to the mash itself, a specific portion of the main mash is removed (usually about 1/3), slowly brought to a boil, then returned to the main mash, raising the temperature of it in the process.

Decoction mashing is renowned for its difficulty. Even though it does take considerably more time, however, there are bonuses to be gained by decoction. Firstly, the boiling of the decoction better gelatinizes the starches, making them more freely available in the mash, so extraction rates are typically higher than with infusion mashing. Also, this same boiling action carmelizes some of the sugars in the decoction, providing the final product with many interesting flavours which otherwise would not be available.

One common and very good question about decoction mashing is this : if I'm not under any circumstances supposed to boil grains when brewing because of tannin extraction, why is this not a problem with decoction mashing. The answer is that when you pull a decoction, you pull as little liquid as possible to boil - you are taking mainly grains. Somehow this extremely thick mash seems to protect against the extraction of tannins.