About 20-30 minutes. The main purpose of boiling sugarcane in water is to release the nutrients in the sugarcane. It usually doesn't take too long, about 20-30 minutes to cook the sugarcane until it changes color and the flesh basically turns dark. If you boil the sugarcane for too long, the sugarcane will be too soft, affecting the taste. If the boiling time is not enough, the nutrients in the sugarcane cannot be fully released, thus affecting its nutritional value.