Roasting of coffee beans

Roasting of coffee beans involves rapid heating, first to drive of the retained moisture, then to raise the bean temperature to about 180 °C.

Some moisture is lost during roasting and carbon dioxide is produced in a comparatively large quantity, some of it escaping and some being absorbed within the texture of the roasted bean.

Roasting releases the oils and acids that give each coffee its unique flavor. The flavor and aroma of coffee are best when it is freshly roasted and deteriorate on standing.

Carbohydrate decompose, caramelize and perhaps in combination with other substances contribute to the aroma of the beverage produce from the roasted coffee.

The type of roast determines whether brewed coffee is mild or strong.

The onset of roasting reactions to be as low as 151 °C and when the bean temperature exceeds 165 °C the reactions have switched from endothermic to exothermic and the roast has begun to fully develop. Theoretically ~700 kJ is needed to roast 1 kg of coffee beans.
Roasting of coffee beans