When refrigerated, why do certain oils (like olive) become solid and others (like canola) don't?
Some oils become thick and viscous at cold temperatures due to fats and compounds called polyphenols suspended in their midst. Because olive oil is minimally processed, it contains more polyphenols than other oils. (Canola oil is usually processed to the point where very few of these compounds remain.) Polyphenols are soluble in oil only at room temperature. As the temperature decreases, they begin to separate out, making the oil cloudy. (For olive oil, this separation occurs at 43 degrees.) Returned to room temperature, the polyphenols will dissolve once again and the oil will look normal. Even so, olive oil takes a few hours to “melt” back into its liquid form once it has been refrigerated, so we recommend storing it at room temperature in a cool, dark place. Once opened, olive oil has a shelf life of about three months.