Everyone knows what water is, but what about malt? Malted grains make up the bulk of a beer recipe. Malted barley is the most common, followed by malted wheat. Other cereals such as oats, rye, corn, and rice are sometimes used as well.
Grains give beer:
"Mouthfeel": How does a beer feel in your mouth? Dry? Sweet? Thin? Creamy? Grainy? Grains contribute to the overall feel of beer on the palate. Some grains are processed for the sole purpose of adding thickness and "texture" to the body of beer. Some grains are less fermentable (harder for yeast to process into alcohol) than others. There are types of grain that will leave components in beer, thickening it without adding alcohol content.
Flavor: Grains can add dark chocolate, biscuit, dough, coffee, caramel, toffee, cracker, wheat, astringent, burnt, sweet, sour, or even smokey pit-BBQ-like flavors to beer. The number of grains available to the brewer are varied. Furthermore, varying their quantities can change the flavor profile entirely.
Alcohol content: Simply put: the more grain the more potential alcohol a beer can have. A beer made with twice the amount of grain can theoretically yield twice the quantity of alcohol. This is why high-alcohol beer are often more expensive: they simply require more material to make.
Color: Grains can be thought of as paints or dyes in the way they affect the color of a beer. All paintings must start out with some sort of canvas or base from which to work off of. In brewing, the "base grain" is used in the largest quantity and other grains, called "specialty grains", are used to add color and flavor. The base grain can be though of as the canvas and the specialty grains as the palate of colors. A grain such as "pilsner malt"(used in pilsners, light lagers, and Belgian ales) contributes a marginal amount of color while a grain like "roasted barley" (a grain that is kilned in ovens until black in color and used in stout beer) will contribute a large amount of darkness to beers, even in small quantities.
Contrary to popular belief, the darkness of a beer does not necessarily denote the alcohol content or even the thickness of a beer. A small amount of dark dye can be used to make a beer dark in color (the German "Black Pilsner" beer called Schwartzbier is made in this way). Alternatively (and less commonly used in brewing) a large amount of lighter dye can darken a beer. The latter approach certainly does contribute massive amounts of alcohol to beer, and the "barley wine" style of beer is made in this way.
Various grains have the been assigned "Lovibond" units according to their color contributions in beer. From the examples above, Pilsner malt is rated at 1-3L while roasted barley can be rated as high as 500L. The Standard Reference Method (SRM) is used to the determine the color of beer. Below I have compiled a sample of some hues and their respective SRM ratings:
SRM values vary from a pale straw lemonade to a jet black opaque. Various styles of beer can be found within this rainbow of colors.
Pilsner beers (Pilsner Urquell, Spaten Pils), American pale lager beers (Budweiser, Bud Light, Miller Light, Coors, etc), Kolsch beers
Belgian Tripels (Chimay White, Tripel Karmeliet, Westmalle Tripel), Blonde and Golden Ales (Duvel, Leffe Blonde)
Bitters (Boddingtons), ESBs (Fuller's ESB, Redhook ESB), English Pale Ales (Great Divide DPA), American Pale Ales (Sierra Nevada Pale Ale, Red Seal Pale Ale), India Pale Ales (Pyramid IPA, Bridgeport IPA), Imperial/Double IPAs (Dogfish Head 90 minute IPA, Russian River Pliny the Elder), Amber Ales (Full Sail Amber, New Belgium Fat Tire), American Dark Lagers (Killian's Irish Red, Shiner Bock, Amber Bock)
Brown Ales (Newcastle), Porters (Boulevard Bully Porter, Fuller's London Porter, Left Hand Black Jack Porter), Barley Wines (Great Divide Old Ruffian, Sierra Nevada Bigfoot, Anchor Old Foghorn), Belgian Dubbels (Grimbergen Dubbel, Westmalle Dubbel)
Dry Stouts (Guinness), Sweet Stouts (Left Hand Milk Stout), Imperial Stouts (Great Divide Yeti), Belgian Abts (Westvleteren 12), Schwartzbier (Köstritzer Schwartzbier)