The most common cause for odor and fruit flies is exposed food waste. Make certain that all food waste is covered. When adding fruit and vegetable trimmings to your pile, dig a hole in the center of the pile and mix in your food waste. Then cover with a layer of brown material (dry leaves or straw for example). If you have a fly infestation cover with dry brown materials and refrain from adding more fruit and vegetable trimmings for 3 weeks.