Mashing is a step in the brewing process that combines crushed Malts with hot water in a mash tun to convert complex starches into simple sugars that are more readily fermented. There are many variations of mashing, but the single infusion mash described below is easily done with home equipment, and suitable for most popular beer styles. During the malting process barley grains develop many enzymes that are needed for mashing. These enzymes, when heated with water in the mash, react with the starches in the malt and produce maltose. Maltose is a favorite food for yeast during fermentation. After the mashing process, hot water is used to extract the sugars from the grain in a process called sparging to produce a sweet liquid called wort for brewing.
Types of Mashing
The most popular mash profile among homebrewers is the single infusion mash, but several methods can be used to mash and all are accessible by the homebrewer.
Single Infusion Mash
The Single Infusion Mash, also called the British Infusion Mash is the simplest mashing method for homebrewers to use. In an infusion mash, room temperature crushed grains are combined with a premeasured amount of hot water at a fixed temperature. By accurately calculating the volume and temperature of the water, one can reach a target temperature for the combined mash in the 148 to 158 F range (64.5-70 C). Infusion is typically done at a water to grain ratio of around 1.25 quarts per pound of grain (1.3 liter per 500g of grain). The easiest way to calculate the proper infusion volume and temperature is with an infusion calculator or brewing software such as BeerSmith. The mash is then held at that temperature usually by keeping the mash in an insulated cooler for 45-90 minutes. At this temperature, the mash will readily convert starches into sugars. You can test for conversion of sugars using an iodine test. Simply draw a small quantity of mashed grains out, add a few drops of iodine to it. If the iodine does not turn blue, then the conversion is complete.
An alternative to the infusion mash is the temperature mash. Rather than adding a known quantity of hot water, the mixed water and grains are simply raised to the target mashing temperature and held at that temperature until the starch conversion is complete. While this is quite practical for a commercial brewer, temperature mashing presents challenges to home brewers. Most homebrewers use simple pots over a stove or propane burner, and it is difficult to hold a precise mashing temperature for an extended period using just a stove and pot.
A third technique traditionally used in Germany for many beer styles is decoction mashing. In a decoction mash, a quantity of mash including both grains and water is moved to a second container where it is brought to a boil. The boiling mixture is then added back to the original mash to raise the temperature of the overall mash. Again, a calculator or brewing software is needed to accurately calculate the correct volume to decoct. Traditional decoctions were typically done at higher water to grain ratios of 2.0 qt/lb or more. More modern techniques often use water to grain ratios closer to the 1.25-1.5 qt/lb range.
Multiple Step Mashes
Though a single infusion mash is suitable in 95% of cases where modern well modified malts are used, some precooked adjuncts and undermodified malts require protein rests at lower temperature before the main saccrification (sugar conversion) step in the mash profile. These protein rests help to break down complex starches in preparation for saccrification. Infusion, temperature and decoction steps may be combined to achieve multiple step mashes. For example a complex three step decoction mash might start with an initial infusion step to an acid rest at 105 F, followed by a protein rest at 122 F, and a saccrification step at 155 F. In many mash profiles, a mash out step is used to raise the temperature of the entire grain bed in preparation for sparging. The mash out step helps to halt saccirifcation, and also helps ensure an efficient sparge by extracting sugars at a higher temperature.
The temperature of mash steps, particularly the main sugar conversion (called the saccrification step) can have a significant effect on the character of the beer. Lower temperature conversion - around 148-152 F will take longer but will produce a more complete conversion of complex starches to sugars resulting in more fermentation and a clean, lighter tasting beer. A high temperature conversion of 155-158 F (68.5-70 C) will result in less starch conversion leaving a beer with more unfermentable dextrines. This will create a beer with a full body and flavor. Middle mash temperatures (153-156 F / 67.69 C) will result in medium bodied beers.
The Acid Rest, a step done early in the mash around 95F (35C) is performed by some traditional brewers to lower the pH of the mash. This was primarily done in very soft water locations like Pilsen that lacked minerals needed to acidify the mash. However modern brewers using most waters do not need to perform this step. Proper minerals and pH adjustment, highly modified grains, and a much better understanding of water chemistry have largely eliminated the need for an acid rest.
After the mash process is complete, the grains, water and sugar are still in suspension in the mash tun. The sugars are separated from the grains in a process called sparging (alternately called lautering) to produce sweet wort. The wort is then boiled and fermented to produce beer.