You should store homemade granola in an airtight container at room temperature for up to a month. I store mine in a kitchen cabinet away from light and heat. There usually isn't any leftovers after that, but if you have leftovers, you can freeze it for up to 6 months. Just make sure it is sealed well, with all air removed from the container. You can crisp the granola in a 200°F oven for 10 minutes or so after it has defrosted.