Coffee Roasting Roasting can be done by oven, stove top, gas or wood fired tumbler, hot air popcorn popper, or by hot air coffee roaster. From 10% to 20 % of the water weight of the green coffee beans comes off during the roasting process. The beans brown as the sugars caramelize with the application of heat. There... Similar Editorial : Coffee Roasting De mystified by Andy White. | Source : Ethiopian Coffee