If your olive oil smells like crayons or old nuts, and leaves a greasy film in your mouth, it's probably gone rancid (you can read more about this here). This can happen due to exposure to air, heat and light — and will eventually happen to all olive oils over time. If you've just received your order and think it's rancid, please let us know immediately, as it may have been exposed to heat in transit (on a hot mail truck, for example). If you've had your olive oil for a while and you think it's rancid, it may be because you've had it open for more than four months, more than a year and a half or two has passed since harvest, or that it has been stored too close to a heat source or direct light.