With slow drum roasting of coffee, green beans are placed in a slowly rotating drum and roasted at a low temperature. This slow roasting process takes longer than conventional roasting and allows the flavors and acids in the beans to fully develop. The roasting goes through various stages, including the drying phase and the Maillard reaction, creating complex flavors. After roasting, the beans are quickly cooled and left to rest before being further processed and used to make coffee. This approach results in a rich and balanced taste experience in the coffee.