Essential oils if stored properly can last for years. Essential oils are chemicals manufactured by plants. During the distillation process, the plant chemicals recombine and form new scents. These scents are valued for their perfume and medicinal value. Care needs to be taken to stop the chemicals recombining into chemicals that can sour the oil's scent.
Heat and water are the major spoilers of essential oils. Make sure to keep the lids on your oils especially in the bathroom or areas where there is moisture. Water can combine with esters in essential oils and create vinegar or other acids that will sour the oils. There is no way to reverse this process once it has occurred and your only option is to destroy the oils.
Heat is created in bottles that are left in sun or in a window. Light enters the bottles and once it moves through the glass turns into heat. Heat will speed the oxidation process and oils will age prematurely. Citrus oils, such as sweet orange essential oil must not be allowed exposure to the sun as they are expressed oils and oxidize rapidly. These oils should be kept in cool to cold environments. Refrigerating them can help them to retain freshness. Once oils have oxidized, their color darkens and they will irritate the skin. Store oils in brown bottles to slow down the effects of light.
Keep oils out of areas that experience high temperatures. Do not leave your oils in the car especially during the summer. Putting them in the trunk will not stop the heat from ruining your oils. Please do not microwave your oils. Heat will speed the oxidation process and ruin your oils causing them to be useless to you. A delightful lavender oil with full ester and alcohol content will sour left in the heat and humidity. A lovely oil will become one that is not tolerable and your only recourse is to throw it away.
Oils kept in air conditioned area out of the light, heat, and humidity can remain fresh and delightful for years. Good care and storage will allow your valuable oils to retain their freshness and medicinal value. With a little planning and preparation, oils can last for years and years.
Pressed oils will oxidize over time. Great care must be taken to retain their freshness. Oils may even be frozen. Cold may allow certain parts of the oil to solidify. The look of the oil can change, but once the oil is allowed to come to room temperature, it returns to its original form. The quality is not compromised. Do not put oils in the oven, a hot window, or microwave to warm them up. This will ruin your oils. Gently warm them to room temperature or hold them in your hands for a few minutes.
There are chemical constituents in essential oils called esters. Esters are a balanced chemical formula. An alcohol combines with a naturally occurring acid, which is often ascetic acid or vinegar. Alcohol combines with acid and creates an ester and water. Esters have a wonderful scent often described as fruity and sweet. If extra water is added to esters or oils containing esters, the water balance is upset and the oil sours. Heat can also disturb the balance and the ester creates vinegar or acid. Now the fruity sweet scent is lost and there is no way to repair this.
With a little care and understanding of how oils work, you can maintain your oils for years. Keep them out of the light, heat, and moisture. Keep the lids on when not in use. Keep oils out of windows and strong light. Keep your oils cool or refrigerated. Keep your oils in dark bottles. Following these few simple rules will allow you to keep your oils for years and years.