Green coffee beans can be roasted at home in a cast iron skillet. Over a medium flame, stir the beans until you hear what will sound like popcorn. A light roasting happens when the coffee finishes the popping sound. In 3 more minutes you should have a medium roast and a heavier roast begins when the beans start to crackle and sizzle. Like a dark roast? Three more minutes and your beans should have a dark, glossy look.