Glass Transition
Glass Transition refers to the process in which coffee beans shift from a hard, rigid state to a more flexible, rubber-like texture due to heat exposure during roasting. This transformation allows the beans to expand and develop a porous structure, but eventually, they revert to a glassy state as roasting progresses.
In specialty coffee, this process is carefully controlled to preserve the beans’ natural flavors. Adjusting roasting temperature and duration helps develop a complex aromatic profile rather than merely altering the bean’s physical structure.
The precise temperature at which coffee beans become more pliable depends on how quickly they lose moisture—typically occurring around 190°C (374°F). Since moisture levels gradually decrease while temperature rises, drier beans require a higher temperature before reaching the glass transition threshold.
