Roasting coffee is the process of heating/cooking/drying coffee beans in a coffee roaster in order to transform the physical and chemical properties of the green coffee beans so the desired flavors and aromas of the final cup of brewed coffee can be achieved.
Chemical Reactions of Roasting – Pyrolisis
Roasting eliminates most of the moisture in the coffee beans and begins a series of chemical reactions known as pyrolisis, changing the chemical composition of the coffee and developing the compounds associated with the flavors and aromas of the brewed coffee.
The Skills of the Roastmaster
The skilled roastmaster strives to apply the proper temperature for just the right amount of time to bring out the best flavors of the particular coffee beans being roasted.
Roastmasters pay close attention to the color level of the roasting coffee beans as they expand and change color, ranging from very light to very dark. As the coffee beans lose moisture, their density also changes.
Effects of Coffee Roasting
Coffee roasting, in various aspects and instances, creates, modifies, and/or stabilizes the fragrance, taste, aroma, sweetness, acidity and body of the coffee.
Coffee Roasters, Roasting Temperature, and Roasting Time
Roasting coffee requires skill as well as a proper coffee roaster. A typical roasting temperature ranges from 370 to 540 °F (188 to 282 °C).
Roasting times vary from about 12 to 30 minutes, and the beans shrink about 20% by weight as they gain a dark hue and fragrant aroma. Twenty-five pounds of green coffee beans may take about fifteen minutes to roast.
As an example, it takes about eight pounds of coffee cherry to make one pound of roasted coffee (100 lbs. of coffee cherry produces approximately 12 lbs. of roasted coffee.
The roastmaster also listens for the popping sounds of the roasting coffee. These distinct "cracks" of the coffee beans occur at particular roasting stages, and there is a first crack and a second crack.
The first crack occurs at about 385 to 400 degrees Fahrenheit, typically just several minutes after the roasting begins. The coffee beans visibly expand in size as they crack, crackle, or pop. Light Roast s are roasted only until the first crack.
The second crack occurs when the coffee beans reach about 440 to 450 degrees Fahrenheit and the cellulose matrix of the coffee begins to break down.
This occurs usually several minutes after the first crack as the coffee beans once again, crack, crackle, or pop. Coffee beans roasted just to this point are usually considered a Full Roast (Medium-Dark Roast).