Optimum recovery of all essential oils by steam distillation requires not only the elimination of reflux flow caused by the delivery of more water than the herb surfaces can hold, but also the existence of conditions which promote the maximum transference of latent heat from the steam to the oil. Since these advantageous circumstances do not occur naturally, the distiller must create them by matching the steam's wetness fraction to the absorptive property of the herb. The aim is to ensure that the herb surfaces remain moist during the whole distillation while retaining some residual absorptive capacity. They must not become flooded before all their oil has been removed.
With simple distilling equipment, where it is not easy to vary the moisture content of the steam, it is necessary to harvest the lavender at the stage of ripeness when its natural moisture content and absorptive capacity are suited to the quality of the steam available.
In more sophisticated distilleries, the judicious management of a good commercial boiler offers steam which ranges from water bath quality with its large wetness fraction for processing very absorptive herb towards the end of the harvest, to steam that is so dry that it can even take up a little excess moisture from herb surfaces that may be too wet early in the season. (Technically that steam would be slightly superheated' as it entered the bottom of the still and would instantly revert to being saturated steam near 100°C as it gathered moisture.)
If the lavender flowers are in good condition and the still is at least 1.3 m tall, the ratio of water to oil in the whole completed distillate should not exceed 20 to 1 by weight. If this is achieved, the steam cannot be too dry. Conversely, if blackened water does not accumulate beneath the charge, the steam is unlikely to be too wet. If the steam's moisture content is adjusted to give a result between those two undesirable extremes, the distillation will be at its most efficient and damage to the oil will be minimal.
Was this article helpful?
You have probably heard the term Aromatherapy and wondered what exactly that funny word, „aromatherapy‟ actually means. It is the use of plant oils in there most essential form to promote both mental and physical well being. The use of the word aroma implies the process of inhaling the scents from these oils into your lungs for therapeutic benefit.