So what actually makes the roasts different, other than just the color?
Simply stated - lighter roasts taste more like the flavor of the original bean, darker roasts taste more like the flavor of the roast.
Light roasts maintain more acidity in the cup. They are thinner, and enjoyed for their ability to allow the flavor of the bean to come through clearly and reveal specific nuances that are distinctive of a country’s origin, such as chocolate or citrus.
Dark roasts are known for their bold flavor and body. Their higher roast temperature will mellow out the bright flavors that a light roast offers and can reveal dark chocolate notes and a creamy feel in the mouth. Dark roasts have the more traditional flavor package that people visualize when they think of coffee.
Medium roasts are the happy middle ground. They can reveal many of the characteristics of origin, while still offering a bold and sweet cup with a lot of depth.
One of the most important and measurable compounds found in roasted coffee is chlorogenic acid. In this case, acid does not refer to acidic flavor, nor pH, but rather to a type of polyphenol compound that is an antioxidant and is known for its various health benefits. A scientific study by Charlotte Mills in Food Chemistry, December, 2013, showed that lighter roasts can have as much as double the Chlorogenic Acid content as darker roasts.
Still haven’t had enough? Check out Roast Science Level: Genius