We've already discussed the fact that the color of a beer isn't always an accurate indicator of its taste, but we can make some sweeping generalizations about what we're drinking based on looks alone: pale beers like German and American pilsners will be crisp and clean; amber beers like doppelbocks and brown ales will be caramelly and sweet; and dark, near-black beers like Guinness and other stouts will be rich and roasty.
Why do these particular flavors come up time and again in beers that fall within the same part of the color wheel? It's all about the malt.
What Is Malt?
Out of the four main ingredients in beer—hops, malt, yeast, and water—malt is the main contributor to the beer's color. And when we're talking about malt in modern brewing, we're really talking about barley most of the time: it's the Goldilocks of grains, providing the right balance of starch, protein, and enzymes to make beer.
To turn barley into malt in brewers' parlance, dried kernels are soaked in water until they start to sprout (anyone who's germinated a seed knows this process pretty darn well). Once the rehydrated barley starts to grow green shoots, it's time to dry out again and get a nice, tasty tan. The malted barley is "kilned"—basically roasted or baked until it gives off enough moisture and gains enough color for the brewer's specifications.
What Gives a Malt Its Taste (and Color)
In greatly simplified terms, the final color (and taste) of the malt depends how long the barley is kilned and how much moisture it retains after kilning. Brewers can choose from a wide range of malts in varying degrees of color and flavor: malts that are more lightly kilned, like pilsner malt or Vienna malt, don't give the beer as much sweetness and body as those that are more deeply kilned—like biscuit malt or black malt.
It's the mixing and matching of all these different malts, as well as balancing them with the right blend of hops and pairing them with the right strain of yeast, that makes brewing as much of an art as it is a science.
So what makes Guinness so dark in color? It's a deeply roasted malt—specifically roasted barley in this case—that gives this most famous of Irish stouts its signature color as well as its dry and coffee-like (but still surprisingly light) flavor profile. As they say, it's a lovely day for a Guinness, so what are you waiting for?