Different coffee bean roasts are just as important to the flavor of your cup as the type of beans that went into your coffee. Overall, beans that are roasted lightly will be sharper and have a more acid overtone than heavily roasted beans. Dark beans are bolder and have a more fully developed flavor, though it is definitely possible to over-roast beans. They'll taste burned or smokey if they have been roasted for too long.\n\n\n\n\n\n\n\n
If you are used to getting one certain kind of bean, just remember that origin of the bean can really change the taste as much as the roast will. Getting an American roasted Ethiopian coffee, and then buying the same roast with Colombian beans will give you a different tasting cup. The roasting process releases the oils inside the bean, which brings out the taste of the coffee. Though it may seem contradictory, lightly roasted beans have more caffeine than dark roasts. The heat cooks off some of the caffeine during the roasting process. For coffee shops and sellers, the terms used for the different coffee bean roasts can vary but there are a set of terms that are generally accepted. Once you know the the following coffee roasting terms, you'll have an easier time buying the roast you like.
Cinnamon - This is the lightest roast usually available, and the beans will be light brown. Oils haven't been released, so the beans are dry and your coffee will have a grainy or baked flavor.
New England - New England is a bit darker than cinnamon but has been roasted long enough to lose the bready flavor. It may be a little sour because the natural sugars haven't been caramelized yet. This roast is more popular in the eastern United States.
American - A fairly standard roast, on the lighter side. American is a common roast more towards the western parts of the USA (hence the name).
Medium City - At this point, the beans are as dark as milk chocolate and is the standard dark roast. Flavors that define the different varietals start to become evident, and the coffee is richer than the previous roasts.
Full City - Beans at this roast will start to have a wet or oily look to them, unlike the drier light roasts. These coffees are sweeter and can have a caramel flavor to them, though that can depend on the varietal.
French or Espresso - Beans at the next roasting level go by French roast or Espresso roast, and they are commonly used when making strong espresso. The beans are very oily and very dark looking.
Italian, Dark French or Spanish - The darkest roasting is nearly burned and goes by various names. This isn't a particularly common coffee roast as the coffee has a burned taste to it and the subtle flavors of the beans are lost.
These terms are important when buying pre-roasted beans, but understanding how the roasts evolve and build flavor will also help you if you are doing your own roasting. When home-roasting, some machines will have settings that can let you choose the precise level you want but otherwise you will have to get the know the look of the right roast and learn when the stop the process.