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Here, re-distillation is carried out at low pressure in order to isolate the various chemical constituents, resulting in a terpeneless or a folded oil.

1. Terpeneless Essential Oils

These are essential oils that are concentrated by removing the comparatively inodorous and therefore (to some!) ‘valueless’ terpenes. The terpenes limonene and alpha-pinene, for example, oxidize readily and this alters their composition, resulting in changes to the aroma and to the therapeutic effects. This tendency of some constituents to oxidize makes storage of certain oils rather difficult. Also, having only slight solubility in alcohol, they give a cloudy appearance to the end product – a drawback to the perfumer and flavourist. De-terpenated essential oils are therefore ‘more soluble, more stable and much stronger in odour’.^8a

Terpeneless oils are not recommended for use in aromatherapy, because not only is the wholeness (and therefore the natural synergy) of the oil destroyed, but it now contains a higher percentage of the other chemical components; some of these may be the more powerful ones with which an aromatherapist has to take care even when present in lesser quantities in a whole oil!

Terpenes are removed by distilling under reduced pressure; as these are the smallest molecules present in essential oils they are the first to evaporate, eventually leaving the terpene-free oil in the distilling flask.

2. Folded Essential Oils

These are concentrated oils, differing from terpeneless oils in that they still contain varying amounts of terpenes. The process is halted wherever the perfumer wishes, with varying, known, percentages of terpenes being removed. The oils are referred to as singlefold, twofold – up to fivefold (where the greatest percentage of terpenes have been removed).^8b

Essential oils are fractionated to remove other constituents too, e.g. bergapten (or bergaptene) which is a furocoumarin, not a terpene (see chapter 3). Fractionated oils are of use only in perfumery and the food industry, although some aromatherapists use bergapten-free bergamot oil because bergapten is the chemical responsible for photo-sensitization (yet use in sunlight is its only contra-indication! – see chapter 6). In my opinion this goes against the basic belief in aromatherapy that the whole, natural, synergistic mix of components, as extracted from the plant, should be used for maximum therapeutic benefit.