Hydrosols

Distilled Or Extracted Specifically For Therapeutic Use - 3 

As one of the students remarked afterward, " I thought I understood the work involved , but this changes everything. I'll remember this for the rest of my life!" And I'm sure she will. Many tabletop distillers are now available, and both science companies and aromatherapy companies offer distillation units for sale  for the home experimenter. Even the Gaggia coffee company makes a still; it looks like a fancy cappuccino machine. In large-scale distillation, the steam is usually created in an outside source, although ancient designs and home stills usually boil the water for steam in the same pot in which you place the plant material. Water boils at one hundred degrees Celsius and at this point changes phase to become a gas, or steam. if the water is placed under pressure, the boiling temperature can be changed, similar to the way that altitude can effect  the boiling point.

In therapeutic distillation the boiling point must be kept at one hundred degrees Celsius so the steam generator and still can operate  under only atmospheric pressure. In industrial distillation the steam is generally superheated meaning that its boiling point is raised under pressure. This has two main functions: First, the hotter steam extracts the volatile components  from the plant material more quickly, and second superheated steam moves more quickly, and second, superheated steam moves more rapidly and under pressure can literally be injected into the stills at an accelerated rate, vastly different from the gentle trickle preferred for aromatherapy products. Thus industrial distillation is shorter, more cost-effective, and concerned with the maximum output for the minimum cost.

Another practice that is more common in industrial distillation, although it has its place in therapeutic distillation as well, is cohobation. Cohobation means simply that the hydrosol or condensed water that comes off the still is recycled. The receiving vessel, called a Florentine flask, has an outflow that takes the water back to the steam generator, where it is reheated and passed through the plant material again. Cohobating the hydrosol means that any microdrops of essential oil that were dispersed in the water have an opportunity to coalesce into drops big enough to seperate into oil, thus improving the overall oil yield of the distillation. Water, which as we know is a precious commodity, is saved and the cost of production further lowered.

In therapeutic distillation, cohobation is used in distilling rose, where many of the four hundred-plus  chemical components are highly water-soluble and the yield of the rose so low that every drop is extremely valuable. Uncohobated rose oil is missing many of the plant's important therapeutic and aromatic compounds because they stay in the water, and therefore it has little value and is never seen. Home distillation units frequently utilize cohobation because the tiny amount of plant material yields so little oil that the extra drops that cohobating can achieve make the process worthwhile. The downside of cohobation is that the resulting hydrosol is nearly useless from a therapeutic point of view, as it contains no dissolved essential oil, and the repeated heating of the water also seems to damage the water-soluble components in the hydrosol. But it still smells nice and is fun to play with. 

Industrial distillation is perfectly acceptable when the resulting oil is to be used only for the extraction of specific compounds. The mono- terpene pinene in some pine oils is extracted for use in artificial apple flavours, scareol from clary sage is in cigarettes , and the camphor in corn mint is used in cold remedies and liniments. However, the extreme heat and pressure of the steam have damaging effects on some of the chemical constituents in the plant material and can " burn" the plant, giving an off flavor or odor to the oil as a whole. Also, essential oils are volatile, so excess heat frequently "boils off" some of the delicate high notes that are desirable in aromatherapy.

Let's look at the production of lavender oil for a minute. Most of the lavender commercially grown in France and other countries is actually a hybrid lavender more properly called lavandin. There are many lavandins: Lavendula hybrida x abrialis, x reydovan, x grosso, to name a few. These are the plants that you see in the stunning photographs of the lavender fields of Provence. Lavandin produces a much higher yield of essential oil than does true lavender (Lavandula officinalis, L. vera or L. angustifolia) usually three to four times the amount. But let's assume that we have true lavender plants to fill our still; what would we need to do to produce the most therapeutic oil possible?

If our still holds between 170 and 200 kilograms and we let it run for one hour, we would get approximately 1 kilogram of lavender oil. This would be true lavender oil, and if it was produced from organic plant material it could honestly be marked  as "certified organic lavender essential oil". This is what many people are buying. However analysis of this oil would reveal that it likely did not contain the full range of the therapeutic chemicals that we want for aromatherapy. Most notably the coumarins would be missing.

Coumarins are one of the main sedative components of lavender oil and are produced only after the first eighty to ninety minutes of distillation. Back to the still. If we leave the distillation to continue after that first hour, for say, another two or three hours, we will have a total output of approximately  1.1 to 1.2 Kilograms. The first hour yields a kilogram and the next two hours one hundred or two hundred grams, an increase of only 10 to 20 percent; it's hardly worth it...or is it? If we analyze the oil at the end of the three -hour run, we will find that the coumarin content of the oil is now around 0.25 to 0.3 percent. A tiny amount, but it is enough to impart the renowned sedative property to lavender oil.

From a therapeutic point of view we must expect our oil to be complete and therefore contain this tiny percent of coumarins, but from a financial point of view we are virtually tripling the cost of the distillations, since the difference in overall yield is so minute.

Reference: Hydrosols The Next Aromatherapy / Suzanne Catty