At some point before we can drink coffee, it has to go from green to brown via the bean roasting. Roasting is a complex, dynamic process, and in specialty coffee especially, a roaster approaches coffees of different processing types and origins differently in terms of ideal roast times and temperatures. Even coffee from the same farm can differ from harvest to harvest depending on how much rain the farm had during a particular season, the level of various nutrients in the soil, etc. Because of this, roasters are constantly on the move to find the best roast to keep coffee as consistent and delicious as it can be.

Most roasteries use drum roasters (like the San Franciscan we have!) that feature a continuously rotating drum and interior fins (kind of like a clothes dryer) in which beans are roasted. The rotating drum helps make sure that the beans do not burn, but are heated evenly throughout the entire roast. A roaster figures out how to best roast a particular coffee by “sample roasting” the same coffee several times while changing different variables like timing of different phases of the roast, temperature, and airflow like in a science experiment - which it basically is! The perfect roast is a combination of airflow, timing, and temperature - these factors affect what flavors are brought out in the coffee. For example, for a dense, natural process coffee a roaster may intensify the first phase of a roast (apply higher temperature for a shorter period of time) while shortening the last phase of the roast to highlight the aromatics and acidity of the coffee. Lengthening the last phase, on the other hand, will let the coffee caramelize, giving it a more smoky flavor.

Tracking the temperature and timing of each phase of the roast

Traditionally, people talk about three broad levels of roasts: light, medium, and dark, even though the temperature, timing, and airflow can vary a lot within these three categories.

Light roast

A light roast is, as its name suggests, produces lighter beans. These beans are roasted for a shorter period of time than medium and dark roasts, up to when the “first crack” happens (the first crack refers to the popcorn-like popping sound that happens at 205 C/401 F). Light roasts are generally more acidic and have delicate floral and fruity flavors that highlight the origin of the coffee.

Medium roast

A medium roast is roasted until before the “second crack,” and results in a profile that is balanced between body and acidity.

Dark roast

This coffee is roasted past “second crack” and results in dark brown to black coffee beans. This coffee exhibits the fullest body and a chocolate, smoky, and more bitter profile that results from the roast. Traditionally, dark roasting was used to mask the bitterness of low grown Brazilian and robusta coffees. This style was brought to the US in the 60s and 70s and famously exported across the US by Starbucks and Peet’s coffee. In the 90s, however, a roaster in Boston began to roast his higher quality coffees lighter. Finding it more sweet and less bitter, the “third wave” of coffee caught on as roasters pushed their bean quality higher and their roasts lighter. Many roasters across the world now roast light emphasizing the origin character of the coffee with more pronounced acidity.

From Bean to Cup Part 5: Roasting