Mash ingredients

Mash ingredients, mash bill, mashbill, or grain bill are the materials that brewers use to produce the wort that they then ferment into alcohol. Mashing is the act of creating and extracting fermentable and non-fermentable sugars and flavor components from grain by steeping it in hot water, and then letting it rest at specific temperature ranges to activate naturally occurring enzymes in the grain that convert starches to sugars. The sugars separate from the mash ingredients, and then yeast in the brewing process converts them to alcohol and other fermentation products.
A typical primary mash ingredient is grain that has been malted. Modern-day malt recipes generally consist of a large percentage of a light malt and, optionally, smaller percentages of more flavorful or highly colored types of malt. The former is called "base malt"; the latter is known as "specialty malts".
The grain bill of a beer or whisky may vary widely in the number and proportion of ingredients. For example, in beer-making, a simple pale ale might contain a single malted grain, while a complex porter may contain a dozen or more ingredients. In whisky production, Bourbon uses a mash made primarily from maize (often mixed with rye or wheat and a small amount of malted barley), and single malt Scotch exclusively uses malted barley.
Variables.
Each particular ingredient has its own flavor that contributes to the final character of the beverage. In addition, different ingredients carry other characteristics, not directly relating to the flavor, which may dictate some of the choices made in brewing: nitrogen content, diastatic power, color, modification, and conversion.
Nitrogen content.
The nitrogen content of a grain relates to the mass fraction of the grain that is made up of protein, and is usually expressed as a percentage; this fraction is further refined by distinguishing what fraction of the protein is water-soluble, also usually expressed as a percentage; 40% is typical for most beermaking grains. Generally, brewers favor lower-nitrogen grains, while distillers favor high-nitrogen grains. 
In most beermaking, an average nitrogen content in the grains of at most 10% is sought; higher protein content, especially the presence of high-mass proteins, causes "chill haze", a cloudy visual quality to the beer. However, this is mostly a cosmetic desire dating from the mass production of glassware for presenting serving beverages; traditional styles such as sahti, saison, and bière de garde, as well as several Belgian styles, make no special effort to create a clear product. The quantity of high-mass proteins can be reduced during the mash by making use of a protease rest. 
In Britain, preferred brewers' grains are often obtained from winter harvests and grown in low-nitrogen soil; in central Europe, no special changes are made for the grain-growing conditions and multi-step decoction mashing is favored instead.
Distillers, by contrast, are not as constrained by the amount of protein in their mash as the non-volatile nature of proteins means that none is included in the final distilled product. Therefore, distillers seek out higher-nitrogen grains to ensure a more efficiently-made product. Higher-protein grains generally have more diastatic power.
Diastatic power.
Diastatic power (DP), also called the "diastatic activity" or "enzymatic power", is a property of malts (grains that have begun to germinate) that refers to the malt's ability to break down starches into simpler fermentable sugars during the mashing process. Germination produces a number of enzymes, such as amylase, that can convert the starch naturally present in barley and other grains into sugar. The mashing process activates these enzymes by soaking the grain in water at a controlled temperature. 
In general, the hotter a grain is kilned, the less its diastatic activity. As a consequence, only lightly colored grains can be used as base malts, with Munich malt being the darkest base malt generally available.
Diastatic activity can also be provided by diastatic malt extract or by inclusion of separately-prepared brewing enzymes.
Diastatic power for a grain is measured in degrees Lintner (°Lintner or °L, although the latter can conflict with the symbol °L for Lovibond color); or in Europe by Windisch-Kolbach units (°WK). The two measures are related by