Malt is the basis of beer. It provides fermentable and unfermentable sugars. Fermentable sugars are consumed by yeast and converting into alcohol and carbon dioxide. Unfermentable sugars, which make a smaller percentage of the total sugar makeup, provide beer with flavor, color, and mouthfeel.
Malt is a grain (typically barley, but can also be rye, wheat, or oats), that has been partially germinated, then lightly kilned. This readies starch reserves and enzymes within the grain for use by the brewer.
Brewers then crack open the barley husks, and perform a mash. A mash is the process of converting starches in the barley into fermentable sugars, using the enzymes readied during the malting stage. Crushed malts are steeped in hot water, at a temperature usually ranging from 148°-158°F, for an hour. Temperature will affect the fermentability of the wort, creating a drier beer when mashed lower, or a more full-bodied, sweeter beer when mashed higher.
After the mash is finished, sweet wort is separated from grain husks using a filter. This filter can take several different forms, such as a large grain bag or a false bottom. Hot water is then used to rinse the grains of any residual sugars. The wort is then collected in the boil kettle, and the brew continues.
Types of Malt
There is a large variety of different malts available, and they can be separated into 5 main categories. The categories are mainly differentiated based on color and usage. The categories are: base malts, caramel/crystal malts, roasted malts, kilned malts, and adjunct grains.
Base malts are the main malts used, as they contain both convertible starches and readily-available enzymes. They take up anywhere from 60-100% of the total grain bill. Various names include 2-row malt, pale ale malt, and Pilsen malt. The differences between them is the specific variety of barley used to make them, which alters their final flavor.
Caramel/Crystal malts are darker, and give the beer sweetness, color, and body. They are processed similarly to base malts, but after kilning are then mashed (to convert starches into sugars), then kilned at a higher temperature to crystallize sugars. Crystallized sugars on these malts are mostly unfermentable, giving the beer additional sweetness and complexity of flavor. Flavors given by these malts range from toffee-like (on the light end) to deep raison or prune flavors (on the dark end). Crystal malts are usually named with an accompanied °L (ex, Crystal 40L). The L stands for Lovibond, and is the measure of malt color. Darker malts have larger numbers of Lovibond. Finally, the differentiation between crystal malts and caramel malts is one of history (crystal used to be only for English malts, caramel for American); these days the two are used interchangeably. Crystal malt usage varies between 0-15% of the grain bill typically.
Roasted malts are closely related to crystal malts, but are roasted after kilning to a much darker color (usually 225L-550L). They give beers a dark brown to black color, depending on amount used. Flavors from these malts range from chocolate to coffee to deep roast flavors. Roasted malts can come either malted (chocolate malts, black patent) or un-malted (roasted barley). Un-malted roasted grains tend to be darker, and are more strongly flavored. Usage for these malts will range between 0-15% of the grain bill.
Kilned malts resemble base malts, but they are kilned at higher temperatures. However, they are not mashed and roasted, as crystal and roasted malts are. Because of their processing, they contain starches that must be converted, but do not contain needed enzymes, therefore they must be mashed along with base malts. They are used to enhance malt flavor, and have several different specific flavors they add to beer. Flavors given include nutty, toasty, honey-like, and intensely malty. They are typically 10-15L in color, and usage is typically 0-15% of the total grain bill. Common examples include honey, biscuit, and aromatic malts.
Adjunct grains comprise anything that does not fall into the above categories. Common this includes un-malted grains such as corn or rice, but also encompasses flaked grains such as barley, wheat, rye, or oats. Similar to kilned malts, these grains contain starches, but no enzymes, thus must be mashed with base malts. They are typically very light in color, often 1-3L, in give the resultant beer enhanced mouthfeel and head retention. Typically, they will be used 0-10%, but exceptions exist to this. German Hefeweizens may include a large portion of flaked wheat, sometimes as high as 60% of the total grist.
Steeping grains are grains in which conversion of starches has already occurred before brew day. Crystal malts and roasted malts are the only malts than can be steeped. Steeping these grains releases converted sugars, giving the extract beer color, flavor, body, and head retention.
The method of steeping is simple. Grains are added to a grain bag while water is heated. The amount of water is not important, though typically it will be directly related to the boil-volume. Temperature is also not critical, though it is best to steep around 150-160°F. The grain bag is added to hot water, and allowed to steep for a period of 15-30 minutes. Stirring the grains will help extraction, and is recommended. After steeping, the grain bag is lifted and allowed to drain as much as possible. The grains are then discarded and the brew moves onward.
Any grain with unconverted starches must be mashed. These include base malts, kilned malts, and adjunct grains. Be careful when using large proportions of kilned malts or adjunct grains, as they do not have needed enzymes. Enzymes only exist within base malts. Thus, kilned malts and adjunct malts must be mashed with base malts.
Additionally, pay attention your base malt when using large amounts of flaked grains or kilned malts. If your base malt is darker (ex. Munich malt), there may not be enough enzymes for full conversion. Base malts have a measure called diastatic power, which refers to the relative availability of enzymes. Darker base malts only have enough diastatic power convert itself, but not other (non-enzymatic) grains. Lighter base malts (and especially 6-row base malts) have a much higher diastatic power, and are particularly well-suited to converting starches from outside sources.
The method of mashing is more complex than steeping grains. The amount of water used, temperature the grain rests at, and amount of time are all factors to be considered. Amount of water will affect the relative distribution of enzymes, changing the speed of conversion. Temperature will affect the specific enzymes being used, creating a more fermentable wort (at lower temperatures) or a less fermentable wort (at higher temperatures). Amount of time is less important, but you do want to let the mash sit long enough for conversion to occur to completion.
The most common method for mashing is to use a grain-to-water ratio of 1.5 quarts per pound of grain, at a temperature between 148°F-158°F (depending on style), for 60 minutes. This simplifies the process and makes a good, quality wort.
After the mash has finished, clear wort is drained from the grains using some form of filter. Typically, the vessel that the mash is performed in will have a filter built-in (usually a large false bottom or long kettle screen). Hot “sparge” water is the used to rinse the grains of residual sugars (sparge is the technical term used for rinsing grains; “Sparge water” is water used for rinsing). The liquids are then combined in the boil kettle, and brought to a boil.
For a much more in-depth guide to malts, Malt by John Mallett is a great resource