Will the freezing or heating of essential oils have an adverse affect on them? What happens when they are shipped during times of extreme weather conditions?
The answer is neither freezing or heating the essential oils in “normal” shipping conditions will damage them. There are a few common sense things to know about heated or cooled oils and why you don’t have to be concerned about certain types of temperature exposure.
The thing you have to remember is that to obtain essential oils in the first place, the plant matter is subjected to heat. Steam usually. Steam temperature (which can vary slightly based on altitude and air pressure if you are a total nerd…) is on average about 100 degrees Celsius or 212 Fahrenheit. Even leaving an essential oil bottle inside a car on the hottest summer day – you are unlikely to reach this temperature. Although dark seats and dashboards can reach very hot temperatures – it is extremely unlikely that your essential oil in a hot car or shipping truck will ever be as hot as it was during distillation. (And on the flip side, there are some distilleries who purposely freeze certain essential oils in order to facilitate separating them from their watery transport…)
If this is true, then why do we say “do not heat your essential oil”? In general, it is best not to heat an essential oil. If the oil is open to the air (as with heated “diffusion” pans, candles, or warming devices) – then various constituents leave the oil at different times. Heat will create a situation where the essential oil leaves the diffuser in an “incomplete” form. Sort of like eating Flour, Eggs, Milk, and Sugar separately does not taste like a cake. Diffusion of separate components of an essential oil, may not carry the same therapeutic benefits we are looking for. Heating of the essential oil creates a situation in which constituents “leave the party” at different times.
There is also oxidation that occurs with oils that are exposed to air contact – and heat generally speeds up the oxidation process. Oxidation is the worst enemy of an essential oil – and suggestions to leave bottles open to “air out” or similar advice to augment an “off” smelling essential oil – is basically allowing the evaporation of more volatile constituents while allowing for additional oxidative damage of the oil to occur.
If your essential oils have arrived to you on a very hot day (or very cold day), or if you have left them in your car, here are some guidelines for how to proceed. The most important thing to remember – is no matter which temperature extreme your oil has encountered, just don’t open the bottle. This is especially important with heat. With cold oils you can open them, and even use them if they will flow. But some cold oils will convert to a more solid state – usually not truly “frozen” but crystallized to various forms. Sometimes partially crystallized oils will have some portions stay in the bottle, while other constituents drip out of the bottle. Basically, giving you an incomplete oil composition from the bottle. With cold oils, usually holding them in your hands for gentle heating will rewarm them to a proper temperature. A very slightly warm water bath can also be used to rewarm your essential oils. Just put the oil bottle (closed tightly) into a shallow dish of lukewarm water. Rock the bottle to mix after the “thaw”.
With hot and heated oils – if you open them, the more volatile constituents will leave quickly. So – just leave the bottle closed and allow it to come to a more normal temperature before opening and using
For oils to stay their freshest, it is best for them to stay cool, and out of direct sunlight. Refrigeration is a great idea if you are very slow to use your oils (over a year once opened).