When beans roast at high heat, their sugars develop; and they begin to take on their accustomed coffee color, aroma, and taste. Pyrolysis – a chemical change brought about at about 405°F – occurs so that the beans' starches convert to sugar. A successful light roast (415-425°F) generates enough sugar to prevent bitterness while allowing the beans' individual, varietal flavor to prevail. All the coffee's sugars are retained, so its varietal characteristics are primary in its final flavor.