Dark roast coffees go by many names - French Roast, Italian Roast, Espresso Roast- but essentially dark roast is the process where raw coffee beans are roasted until they are dark and chocolaty looking. Most espresso drinks are made with dark roasts.
The roasting process changes the taste completely from the taste associated with the origin of the beans. They take on more flavors of the roasting process itself, taking on a smokey and sometimes bitter taste. The little known fact is that dark roast coffee has less caffeine than a lightly roasted coffee. The caffeine levels decline during the roasting process, which takes the beans to a temperature of around 240° C.
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Allen