Coffee Roasting 101

roasting coffee

Roasting is an art as well as a science. It takes time, skill, and patience. Although there are specific formulas for roasting coffee, one must acquire hands-on expertise to properly regulate roasting time, temperature, and airflow.

At Millcreek, we use 12 and 25-kilo Probat roasters. Using smaller roasters allows us to roast daily, in small batches, upon demand. We can customize the roast to suit our style. It gives the roast master more hands-on control. The roast master uses sight, smell, sound, and temperature to determine when a degree of roast is accomplished.

The roasting process converts starches stored in the bean to sugars. There are more than 300+ aroma compounds that exist in the beans with 650+ that are created when roasting. The following stages occur during the roasting process:

  1. Coffee beans are transferred from the hopper to the drum. They start to absorb heat from the drum. Coffee beans turn from light green to dark green as moisture is drawn to the surface.
  2. As moisture is lost, the bean turns yellowish-brown.
  3. At the stage where sucrose, the principle sugar in coffee, reaches the melting point, caramelization begins. Pressure inside the bean caused by a chemical reaction of water and carbon dioxide produces an out-gassing known as first crack, and the beans make a noise similar to popcorn.
  4. The beans now turn from absorbing heat to releasing energy. The beans continue to darken turning from yellowish-brown to light brown.
  5. Beans can continue to roast through various stages. At City roast, the bean will go through a second crack where CO2 is released.
  6. Further roasting releases oils to the surface of the bean.
  7. The roasted coffee is immediately air-dried in a rotating cooling tray.
  8. When roasted, coffee loses 20% of its weight, but doubles in size, while changing color from light green to deep brown.

We match the degree of roast with the characteristics of the specific bean to bring out its best flavor qualities. The lighter the roast, the more the flavor of the bean can be tasted. As the roast gets darker, the flavor of the roast is more apparent. Darker roasts have a tendency to be less acidic because of the structural breakdown.
Blonde or Cinnamon Roast: Beans are dropped prior to second crack and have a slightly wrinkly appearance. The high acidity of Blonde Roast is generally perceived as a lemony, citrusy or sour taste.
City Roast: Beans are smooth, and the roast is dropped at the beginning of the second crack, when the coffee is making a sound similar to popcorn as it gives off its own heat and suddenly expands, thus making a cracking sound. This roast enables the flavor of the coffee to be tasted rather than the flavor of the roast.
Full City Roast: Beans are smooth and shiny, and the roast is dropped slightly after the beginning of the second crack. This roast also enables the flavor of the coffee to be tasted instead of the roast.
Full City Plus / Viennese Roast: Beans have many spots of oil and are dropped mid-second crack. This roast is where, depending on the coffee and its characteristics, the roast starts to become a factor in the flavor of the coffee.
French Roast: Beans look oily before they are dropped to cool. The flavor of the roast is tasted more than the coffee’s flavor. Beans that are French roasted are usually a more mild tasting. Darker roasts have a tendency to be less acidic because of the structural breakdown.
Italian Roast: Beans are rather spotty with oils, and the second crack is over. The taste profile of the brew is a lot milder than a French roast and imparts a smokiness to the brew. There are virtually no acidic characteristics left.


coffee roasting