We get many questions about freezing olive oil, including “does the way it freezes say anything about quality”? The simple answer is no. But, there are two common misconceptions about how extra virgin olive oil reacts to cold temperatures and what the reactions might indicate that we’d like to address in this month’s column.
First, many people think that if extra virgin olive oil gets “hard” or solidifies when kept in the refrigerator, it proves it is extra virgin quality. Not true. Conversely, others think that if extra virgin olive oil solidifies, it must have saturated fat in it. Also, not true. To answer both questions, we have to delve a bit deeper into what makes olive oil solidify in cold temperatures.
Chemistry texts list the freezing point of pure oleic acid at around 39°F. Most manufacturers preset refrigerator temperatures to around 37°F. Olive oil manufacturers don't generally list a freezing temperature because it is quite variable depending on the olive variety and ripeness of the olive at processing. Unlike the properties of a simple compound like water, olive oil is made up of hundreds of chemicals, many of which change with every extraction and affect its freezing point.
In large-scale production, a processing practice called “winterizing” has the biggest effect on how olive oil will react under cold temperatures. Like most fruit, olives have waxes on their epidermis (epicarp) to protect them from insects, desiccation, and the elements. These natural waxes are what allow an apple to be shined, for instance. If an oil is to be sent to a cold climate, or if a refined oil is used in a product like cheap salad dressing where it will be stored in the refrigerator, it is often "winterized" (chilled and filtered) to remove the waxes and stearates. As a result, no clouding or crystals occur.
Oil that has not been winterized will clump and form needle-like crystals at refrigerator temperatures as the longer chain fats and waxes in the oil congeal, but the oil will not usually harden completely unless chilled further. Some olive varieties form waxes that produce long thin crystals, others form waxes that congeal into rosettes, slimy clumps, clouds, a swirl of egg white like material, or white sediment that the consumer may fear represents spoilage. These visual imperfections also may form outside the refrigerator during the winter when oil is exposed to cold temperatures during transport. The white color in the hardened oil does not indicate spoilage, but it is merely an indication of the longer chain fats congealing.
Another myth to dispel is that, if olive oil solidifies under colder temperatures, it must contain saturated fat. But the truth is that all fats will harden if they get cold enough, whether they are saturated or not. As we saw above, olive oil often hardens, but not because it is saturated. It is most often because it has not been refined as seed oils are, to remove waxes. The presence of waxes does not make the olive oil saturated or unhealthy; it just means it is a natural product.
As a general rule, the more saturated the fat, the more likely it will be hard at room temperature. Beef and pork lard, margarine, butter, and the saturated tropical fats in cookies, packaged foods, and snack foods are all solid at room temperature. This improves their shelf life, makes packaging easier, and improves "mouth feel" but is not necessarily good for your health.
Most importantly, chilling or freezing olive oil does not harm or diminish its quality. The oil will simply return to its normal consistency when it is warmed. The ideal temperature to store olive oil to reduce oxidation but to avoid clouding is around 50°F.