The mashing process is the key to all-grain brewing. During the mash, hot water breaks down the long-chain carbohydrates and proteins provided by malt into simpler, smaller units that serve as food and nutrients for yeast during the fermentation process. Furthermore, the proteins and sugars that are created also affect the body, head retention, aroma, and flavor profile of the finished beer.
There are three basic mashing styles, usually referred to as infusion, temperature program or step, and decoction. Within each of these mashing styles there are subtle variations in techniques that offer myriad combinations for creating sweet wort from grain and water.
Any mash program will likely result in a satisfactory conversion of starches. But to determine which mash program is the best particular one for you and the beer you are brewing requires a little bit of knowledge about how and why each of these styles evolved and its effect on the finished beer.
It is also important to realize that while certain beer styles are created most easily by using the appropriate mash program for that style of beer, historically many of the characteristics of the styles in question evolved as a result of the mashing techniques used, not the other way around. Particular mash styles evolved in response to three major variables: Equipment, technology, and ingredients available. This is where you should begin when determining which mash style will work best in your own brewing,
In the single-infusion mash a known quantity of water at a known temperature is combined with a known volume of grain at a known temperature. Through the use of temperature charts or formulas, this results in a very consistent method of obtaining repeatable mash temperatures that are accurate within a few degrees. By shifting variables such as the temperature or volume of the strike water (the water into which you mix your grains), the final temperature of the mash can be adjusted up or down.
Advantages: This style of mashing is the simplest, requires the least amount of additional equipment, and uses a less expensive vessel. As such, it is usually the style used by homebrewers when they first make the move to all-grain or partial-mash brewing. Since heat is not applied directly to the mash, it is efficient to mash and lauter (remove the wort from the grains) in the same vessel. This mash/lauter tun combination can be as simple as a plastic bucket fitted with some form of false bottom and perhaps insulated to help maintain conversion temperatures as accurately as possible for the duration of the conversion process.
Minor adjustments to the strike and rest temperatures can be made by adding small amounts of cold or hot water to adjust a degree or two up or down. Conversion usually takes 30 to 60 minutes, so there is not as much time added to the brewing process as there is with some of the other mash programs such as step or decoction. Once the infusion of mash and water is complete and a consistent rest temperature is achieved, very little attention is required and the brewer is free to perform other activities such as cleaning, sanitization, or household chores to help speed up the rest of the brew day.
The lack of special equipment required for single infusion mashing also makes this the mash program of choice for the majority of small brewpubs and homebrewers today.
Disadvantages: There are primarily enzymes at work in the mashing process, and each one has its own optimal temperature and performance range. Manipulation of these different enzymes also provides a different character to the sweet wort and hence, the finished beer. Since the strike temperature is going to be pretty close to the rest temperature of the mash, most infusion mashes are done at a compromise temperature usually somewhere around 147 to 156 °F (65 to 69 °C). This results in a relatively fixed fermentability level; as a result, mash efficiency, or the measure of sugars produced in the mashing process, usually suffers.
The inability to mash out (raise the mash to a temperature of 170 °F/77 °C to inactivate enzymes and decrease wort viscosity) further reduces the solubility and increases the viscosity (its thickness compared to water) of the wort, further decreasing mash/lauter efficiency. Since the mash will take place at a compromise temperature, it is imperative that only highly modified malts with a well-developed level of enzymes are used. This will help maximize the yield of the mash.
History: Infusion mashing was attractive to early brewers. Only one vessel was required to be heated. This one kettle could do multiple duty by heating the strike water, then later be used for boiling the wort. Early infusion mashes most likely did not incorporate any form of sparging, the process of spraying the grains with hot water to rinse as much malt sugar as possible. The sweet wort was simply run off into the kettle. The mash might have been saved to later be reinfused with more strike water for a second run-off of a weaker style of beer.
Later, as sparging was incorporated into the lautering process, the sparge water or hot liquor could be heated in the kettle and transferred to an insulated holding vessel until it was required for sparging. Almost any style of beer can be produced from any mash program, but those styles of beer such as British pale ales, stouts, porters, bitters, and brown ales that usually use highly modified pale malts are good candidates for single-step infusion mashing.
Temperature program or step mashing differs from single-infusion mashing in that numerous temperature rests can be incorporated in the mash schedule. Resting the mash at a series of successively higher temperatures allows a wider variety of enzymes to work within their own optimal temperature ranges for a set amount of time. This results in more control for the brewer over the final characteristics of the sweet wort and the ensuing beer.
You can raise the temperature of the mash through the use of a mash tun to which heat can be applied or through repeated infusions of hot water to successively raise the mash to the appropriate rest temperatures.
The beta-glucan rest occurs at 118 °F (48 °C) to reduce wort viscosity caused by gummy beta-glucans. This is especially important when using flaked barley, oats, and rye, as well as lightly modified malts.
The beta-amylase rest occurs at 135 to 140 °F (57 to 60 °C) to increase wort fermentability, while the alpha-amylase rest takes place at 158 °F (70 °C) to “convert” the mash.
Two rests no longer used by most commercial brewers are the acid rest at 110 °F (43 °C), which was formerly used to adjust mash pH, and the protein rest at 122 °F (50 °C), which current research indicates has no value.
Advantages: In this form of mashing, the brewer has a greater impact on the finished beer than he or she does using single infusion. Varying the times spent at the various optimal rest temperatures — or deleting certain rests entirely — dramatically varies the resulting sweet wort, even if the grain bills are identical. Also, since a wider variety of enzymes can be brought into play at their optimal temperatures, mash efficiency (the percentage of sugars from the grain that make it into the wort) usually improves. As a result, the degree of modification of the grains is not as critical, and hence a wider variety and quality of grains can be used. If you use a step-infusion program, you may not need equipment in addition to that used for the single-step infusion, providing the mash/lauter tun is large enough to hold the full final volume of the mash.
Disadvantages: Because a wide variety of rests and enzymes can be incorporated into a step-mashing program, it is important to have a clear understanding of what the performance characteristics of the various enzymes are and how they affect the finished product. You can refer to most brewing texts with an extensive section on all-grain brewing for a more complete understanding of these temperature rests and the enzymes at work (but be prepared for a little chemistry).
The mash temperatures can be raised in one of two ways. If successive infusions of hot water are introduced to raise the temperature of the mash, the mash usually will start out relatively thick and by the last step be rather thin and watery; this reduces the specific gravity of the wort and can be detrimental when brewing stronger beers. If you raise the temperatures by directly applying heat to the mash, a mash tun that can be heated is required.
Because the purpose of step mashing is to incorporate additional rests, it usually takes more time overall than the simpler single-infusion technique. Also, most single-infusion mashes benefit from being left alone during the rest period, allowing the brewer the time to perform other duties such as heating water or sanitizing equipment. But a step-mash program requires continual monitoring of the mash and stirring to ensure that each rest is accurately reached and that the temperature is even throughout. In short there are more variables to be controlled and taken into account, and there is more work to do. However, many styles of beer that focus on malt complexity, such as the various Belgian strong styles, and styles incorporating wheat in the recipe can benefit from a step-mash program.
Decoction mashing is a form of step mashing in which the brewer removes a portion of the mash, usually about one-third of the thickest part, leaving behind as much of the liquid as possible. This thick decoction is placed into a separate kettle, where the temperature is raised until the decotion boils. Then the decoction is reintroduced into the main mash, thereby raising the temperature of the whole mash to the next step. This entire process can be repeated as many as three times to incorporate the same temperature rests discussed in step-mashing.
Advantages: When the thick grain portion of the mash is boiled, a physical breakdown of the starches and proteins results, giving the enzymes present greater access to them. This results in a greater conversion rate (more starches are converted to fermentable sugars) than with other mash methods, particularly when low-modified or undermodified malts such as Pilsner and lager malts are used.
In addition, many homebrewers feel that the best way to produce very malty and complex brews is to use decoction mashing.
Because the boiling point of the decoction is fixed, its reintroduction to the main mash results in surprisingly consistent temperature rests. This helps to avoid the tendency to overshoot temperatures when step mashing using a heated mash tun to raise the temperature.
Disadvantages: This is by far the most laborious and time consuming of the mash programs. A typical decoction mash program can easily be two hours or longer. Extra kettles are almost mandatory, as is a high-output heat source that can be accurately controlled to prevent scorching the mash. The decoction and main mash requires constant monitoring and stirring to ensure accuracy and to prevent any scorching or burning of the mash.
History: This style of mashing evolved in Europe, where the malts available at the time were less modified than British malt. The decoction method allowed brewers to consistently perform multi-temperature mashes before the advent of the thermometer and to use the boiling methods to achieve these various temperature rests all physically degrade cell walls present in undermodified malt. This method most certainly developed empirically. Not only did it pre-date the thermometer, it also pre-dated our modern understanding of enzymes and malt modification.
In addition to these three methods, many commercial breweries that incorporate a lot of cereal adjuncts in their recipe formulations use a form of mashing that is a combination of decoction and infusion techniques.
To use large amounts of adjuncts such as corn or rice effectively, these unmalted grains must first undergo a process called gelatinization. The hard, starchy interior of the grain is cooked down to make it available to the enzymes in the malted barley for conversion.
After undergoing this cooking process, the adjunct cereal grains are then infused into the main mash. They help to raise the temperature of the mash while at the same time contributing large amounts of gelatinized starches for conversion.
In such a process it is common to employ six-row pale malts both for their high levels of enzymatic potential as well as for their ability to aid in the lautering process due to a greater husk-to-starch ratio.
Keep in mind with all mashing programs that the natural process of converting starches to sugars takes place over a range of temperatures and not just at one set point. No matter which style of mashing best fits your equipment and ingredients, fluctuations of a few degrees will probably not ruin the resulting beer. They likely will make it only slightly different than what you might have been searching for.
Always keep good notes when mashing (and throughout your brew day in general), taking care to record mash temperatures, water temperatures, and mash rest times. In doing so you will have a history of what worked and what did not, which will provide a wide influence over the finished beers you create, and also a great reason to keep trying new and different mashing techniques.