Coffee is generally roasted between 204 - 218C (400 - 425F) (the longer the beans are roasted the darker the roast).
There are generally three main coffee roasts: light, medium, and dark. The levels of roast usually refer to how long the coffee bean was roasted or exposed to heat. The roasting of coffee beans removes moisture from the inside through evaporation. You can usually tell the difference between the roasts through the darkness of color, texture, surface feel, and weight of the coffee beans. Each roast also has its own flavor and taste.
Medium roasted coffee beans are brown colored and can sometimes have oil on the surface. These beans are heated until about 400-430 degrees Fahrenheit and create beans that have a more balanced overall flavor in terms of acidity and body. Medium roast coffee beans contain more caramel sweetness and darker flavors compared to the light roast, and it's not as bright or acidic as the light.
Medium roasts, like our quality instant coffee, are one of the most popular types of coffee beans because people enjoy its middle-ground balance between the acidity of the light roast and the deep flavors of the dark roast.
Dark roasted coffee beans are dark brown, almost black, in color, and have an oily surface. The beans are heated up to 430-450 degrees Fahrenheit and which creates beans that don't contain much of the coffee bean's original characteristics. A dark roast makes a cup of coffee with low acidity, heavy body, and overall bolder and deeper flavors. These types of beans are not as diverse in terms of flavor and are more uniform containing mostly chocolate, caramel, and nutty flavors. In terms of light roast vs. dark roast, they are completely different from each other.
The light roast is lighter and more acidic with fruitier and floral flavors while the dark roast has darker and smokier flavors. To purely enjoy the differences in taste, you should drink the light and dark roast coffees side by side without any cream or sugar.