Miso should be stored in an airtight container in the fridge, freezer, or any cool dark place, and you can cover it in plastic wrap to prevent any oxidation that will affect the color over time. Also, note that miso continues to ferment while in the fridge, which may change its flavor, and if that happens, add the paste to salad dressings, pickled tofu, stir-fried dishes, or mayo to mask its sourness.