Essential oil is composed of many substances. Even the minor components derived from oxidation or other degradation reactions may have a strong impact on the flavor and aroma value [i].

Mesa Lavender Farms lavender essential oils are produced following the steps outlined in this review. Our oils are available at

Harvest time, plant health, soil fertility, growth stage, climate, etc. affect the chemical composition of the oil. The moisture content of plant material when distilled also plays a role. Additional chemical changes such as oxidation, hydrolysis, and exposure to light and heat can occur during distillation and storage causing even more changes. Reflux can result in a loss of up to 50% of the potential oil.

[i] Grosch W. 2007. Key odorants of food identified by aroma analysis. In: Ziegler H, editor. Flavourings. 2nd ed. Weinheim, Germany: Wiley-VCH.p 704–43.

Essential Oil Components
Figure 1 Stability of Essential Oils: A review. Turek, et al. 2013


Isomerization – chemical change; same formular, different arrangement

Oxidation – compound gains oxygen, loses hydrogen, or loses electrons

Dehydrogenation – chemical reaction that involves the removal of hydrogen

Hydrolysis – decomposition where water breaks chemical bondsHydrolysis - Decomposition where water breaks chemical bonds

Polymerization – combining molecules into larger molecules – includes hydrolysis

Thermal rearrangement –

Claisen Rearrangement


The most common factors causing degradation for lavender growers are:

  • Hydrolysis
  • Oxidation
  • Light
  • Temperature,
  • Reflux


  1. Results in the breakdown of components
    • Unpleasant odor
    • Unbonded water in suspension is absorbed and ruins oil’s keeping quality
  2. Must remove water from essential oil as soon as possible after distillation. Water will appear as bubbles at bottom of collection container.
    • One recommendation is to allow the oil to breath
      • Results in loss of top notes
    • Freezing is typically used to remove water.
      • Place essential oil in freezer. Pour off oil from ice.
        • Not totally effective – ice crystals can be suspended in oil
      • Increases oxidation – Henry’s Law
    • Use dehydrated sodium sulfate
      • Shake into oil
      • Shake container until sodium sulfate absorbs all water
      • Pour off oil through unbleached coffee filter

Oxidation – loss of electrons

  1. Results in skin sensitizing compounds. Allergic contact dermatitis. [i]
    • Can increase production of hydroperoxides.
      • Limonene exposure to oxygen results in hydroperoxides which have a “far stronger sensitizing potency than the pure compound”. [ii]
    • Resulting free radicals “steal” electrons from the lipids in cell membranes, resulting in cell damage.
    • Free radicals may cause aging, pain, affect mood negatively, damage health, cancer and various sicknesses and diseases.
    • Pure compounds are not allergenic, but their oxidation products can cause contact allergy [iii]
    • “Radicals possess an unpaired electron, which makes them highly reactive and thereby able to damage all macromolecules, including lipids, proteins and nucleic acids.” [iv]
  2. Use food grade Nitrogen gas during the distillation, oil water separating, and storage procedures
    • Heavier than oxygen
    • Add to separator
    • Add to essential oil collective container
    • After removing water, top off storage container
  3. Henry’s Law – see temperature discussion


  1. Ultraviolet and visible light accelerate autooxidation resulting in alkyl radicals.
    • Breakdown of essential oil components
    • Transformation of compounds
  2. Monoterpenes rapidly degrade under light energy
    • The therapeutic and olfactory properties of lavender essential oils are attributed to monoterpenes.

      • Limonene – Cancer prevention, inhibition, and regression [vi]
      • cineole – found to reduce colon inflammation in rats [vii]
      • camphor – Relieves Pain and Swelling [viii]
    • [v]Monoterpene abundance changed during flower development [ix]


  1. Chemical reactions accelerate with increasing temperature (Arrhenius equation).
    • Increase of 10o C (18o) results in a doubling of chemical reaction.
  2. Lavender peroxides increase at 5o C (41o) as opposed to room temperature
    • Peroxides have unpleasant odors
  3. Henry’s Law
    • Oxygen solubility of essential oils is higher at lower temperatures
    • Low temperature results in more oxidation
    • Half-filled containers with oxygen in the free space has more oxidation than completely filled containers. However, oxidation still occurs unless oxygen is removed. [x]

Metal contaminants

  1. Impurities of metals can be released into essential oils.
    • Lavender is considered reactive with metals
    • Equal to light and heat, copper and ferrous ions:
      • Promote autooxidation, especially if hydroperoxides are present.
  2. How to Prevent:
    • Use food-Grade Stainless steel still.

Reflux – Results in loss of oil and reduction of quality. Instead of moving with steam into the condenser, oil drips down into the pot. Up to 50% of potential oil can be lost due to reflux.

  1. When inadequate steam is produced to move the essential oil up the charge.
    • Should have first drop of condensate appear within 5 minutes of placing charge in still.
    • Typically need a rolling boil before placing charge in still.
  2. When the distance between the water in the pot and the charge is not adequate and splashing of water into the charge occurs.
    • Space between the water and herb should have a depth equal to one-fifth of the still’s diameter. May need a baffle system to prevent splashing.
  3. Indications:
    • Determined by change in color of water in pot.
    • If water drips from charge when removed from still.
  4. How to prevent
    • Ensure water in pot does not exceed the critical level mentioned above.

Notes on Degradation of Essential Oils

Reference for Notes on Degradation of Essential Oils

[i] Grosch W. 2007. Key odorants of food identified by aroma analysis. In:Ziegler H, editor. Flavourings. 2nd ed. Weinheim, Germany: Wiley-VCH.p 704–43.