The lightness or darkness of a roast describes the degree and duration of the roasting of a coffee bean. While it is not the most important factor in a bean’s flavor, there are similar characteristics presented in beans roasted to the same level, both in the color and texture of the beans and the taste of the coffee they produce.
It’s not just a matter of taste, there’s a difference in the amount of caffeine per cup also, with lighter roasts containing more caffeine than dark. This is because the roasting process eviscerates the caffeine naturally present in the beans.
The roasting process, if followed all the way to the darker roasts, contains two key releases of energy known as first and second ‘crack’. These events known as cracks are sort of landmarks on the roasting journey, periods of the quickest change in the consistency and flavor of the bean.
Light roasted beans are those most similar to the natural state of coffee, they are light in color and there is none of the oily exterior associated with the darker beans. They simply don’t get hot enough while roasted to release any of the oils.
The temperature a light roasted bean is heated to is between 356-401F, around the beginning of the first crack. The beans are cinnamon colored (light roast is often termed cinnamon roast for this reason) and quite earthy and acidic in flavor.
Light roast coffee is usually the best way to achieve higher caffeine content, and a brighter more “fruity” flavor. In fact when you make drip or percolator coffee it’s your only shot and getting the cherry notes out of the bean.
Medium roast describes beans that have been heated to around 410-428F, between the first and up to the beginning of the second crack. This type of roast produces beans of a darker color but sharing the dry and non-oily texture of the light roast. The medium roast is the most common served in the US, and contains a balance of the beans’ natural flavor without so much acidity.
Medium dark roasted beans are heated to a temperature of between 437-446F, up to the middle of the second crack. Beans roasted to medium-dark have a light coating of oil and a rich deep brown color. They are characterized by a heavier body than the lighter roasts and a slight bittersweet aftertaste.
These beans range between chocolate color and almost black, they are oily and have a slight charcoal taste. They are roasted to temperatures of at least 464F, the end of the second crack. If roasted to the extreme end of the scale, the beans become thin and taste burnt, bearing little resemblance to light roasted beans.
Overall roast level tends to be a matter of personal preferences. One thing is for sure though, once you roast your coffee bean it’s shelf life is reduced dramatically. That’s why most people and coffee roasteries only roast small batches at a time.
In general, the lighter roasts are more popular in the US and the darker roasts are more common in European countries, with the darker roasts often used to make espresso and therefore espresso based coffees.
For a better idea of the differences in roasting levels, this analogy can give a bit more perspective.