Why is the glass transition important during roasting?

The glass transition is an important phenomenon during the roasting process because it relates to how the physical properties of the coffee beans change at elevated temperatures, particularly concerning moisture content and structure. During roasting, the beans undergo a transition from a rigid and glassy state to a more pliable, rubbery state. This change allows for the build-up of pressure within the beans as water vapor and gases are released.

As the temperature increases, the starches in the coffee beans gelatinize, and various chemical reactions, including Maillard reactions, occur more readily. The build-up of internal pressure not only facilitates these reactions but also contributes to the expansion of the beans and the development of aroma and flavor compounds. This dynamic adjustment is crucial for achieving desirable characteristics in the final roasted coffee.

While flavor extraction, rapid cooling, and color changes are essential aspects of the roasting process, the glass transition primarily supports the pressure dynamic and the ensuing chemical transformations, making it pivotal to understanding how roasting affects coffee quality.