What next in the process? Well, initially, after distillation our lavender oil has a “rough” odour to it – some people have described it as an intense, sharp, hay, perhaps a bit rubbery, smell – and it isn’t very pleasant. There is some evidence that distillation in or over copper helps this. We distil in stainless steel and our pure lavender oil needs to be matured for about six months to remove this smell before we can use it. During this time it is amazing the change that takes place. When we come back to the oil it smells sweet, floral, herbaceous, fruity – delicious.
The storage conditions of distilled oils vitally important. The enemies are water and oxygen in the presence of excess heat and light. Oxidation reactions can occur that lead to the degrading of the oil, and it “going off”. Light and heat accelerate these reactions. The oil is first dried using a special drying agent. It is then filtered and weighed into large glass bottles. The bottles are filled to the top to minimize the air pocket (with oxygen in the air), and the lid tightly sealed on which stops both air getting in and the oil evaporating out. To further minimize any damaging reactions, the containers we use are made from darkened glass, and once filled they are stored in a cool cupboard. We continue to leave the oil stored away safely until we need it, which can be from six months to two years after distillation.
When oils go off they usually go darker in colour and smell “sour”. The same sort of degrading reactions can occur in your perfume or aftershave. The worst thing you can do is leave your expensive perfume on a sunny windowsill – far too hot and light. At least keep it in it’s box, and preferably cool. I know people with collections of fragrances – they wear different ones depending on their mood and the occasion – and they keep them in a fridge. A bit cold when applying but it really extends their life!
The yield is the weight of oil divided by the weight of plant material, and expressed as a percentage. There are many factors that affect the oil yield. How the lavender is cut - short stems produce a higher yields. Whether the lavender has dried out before distillation. The variety of lavender, growing conditions, the overall weather of the summer season, the weather on the day of harvesting and I daresay the time of harvest. We certainly find that hot summers produce much greater oil yields than those of dull, wet, cool summers.
The “English” lavender (L. angustifolia) seems to produce a yield of about 0.4% to 0.7% by weight. To put these yields into perspective, if we fill the still with 80kg (12.5 stone and a pretty big pile) of lavender stems we will extract out approx. 450g of lavender oil – that’s about three coffee cups, less than a pint! You can see that the oil obtained is small compared to the weight and the work that goes to growing and harvesting the plants!
For the lavandin (L. x intermedia) the oil yield is much higher – about 1.5% – and again is affected by many factors. This higher oil yield for the same work and roughly the same acerage (actually you probably get about 20% more weight of flowers from a given area of lavandin compared to lavender) explains why lavandin oil is quite alot cheaper than “English” lavender oil. This difference in price is largely responsible for the different ways the two oils are used in the perfumery industry.
In another blog I’ve explained the differences between Lavender and Lavandin oil
That’s the end of a series of posts about how we process our lavender to produce the oil. My next post is about what is actually in lavender oil, and how we find this out.