Deep baking. Coffee beans themselves carbonize to black and have a strong bitterness. Among the three baking degrees commonly used in the market, the Italian coffee beans that make espresso are mostly deep roasted. One of the keys to a good cup of espresso is the mixing of coffee beans. Deep baking is at the end of the second explosion in the baking stage. Deep roasted coffee beans have a dark brown appearance and a layer of oil on the surface. The taste will be bitter, without sour taste, and the burnt taste will be heavier.