Essential oils
Practical Action
The quality of the oil obtained from a particular species will be influenced by where it is grown
and how it has been processed. New producers are likely to meet with resistance from buyers as
this is a very conservative market depending to a great extent on trust regarding supply and
quality. Producers and buyers also closely guard information and “secrets”. Once established
trading relationships are made, however, reliable markets can be gained.
Essential oils can be divided into two broad categories:
Large volume oils which are usually distilled from leafy material such as lemon grass,
citronella and cinnamon leaves. Lemon, lime and orange oils are also produced in very large
amounts.
Small volume oils which are usually distilled from fruits, seed, buds and, to a lesser extent,
flowers, e.g. cloves, nutmeg, coriander, vetiver and flower oils.
Harvesting
Correct harvesting is very important. The essential oil content varies considerably during the
development of the plant and even the time of day. If the plant is harvested at the wrong time,
the oil yield or its quality can be severely reduced.
Essential oils are usually contained in oil glands, or veins that are fragile. Poor handling will
break these structures and release the oils resulting in losses. This is the reason a strong smell
is given off when these plants are handled. Some examples of harvesting of common oils are:
Citronella and lemongrass. The first harvest can take place 6-9 months after planting. Then
the grass can then be harvested up to four times a year. If harvested too often, the
productivity of the plant will be reduced and the plant may even die. If the plant is allowed
to grow too large, the oil yield is reduced. For lemongrass it should be 1.2m high with 4-5
leaves. The grass should be harvested early in the morning as long as it is not raining.
Harvesting can be done with machetes or simple knives.
Cinnamon bark is harvested during the wet season since the rains facilitate the peeling of
the bark. Harvesting involves the removal of bark from stems measuring 1.2-5 cm in
diameter. This takes place early in the morning.
Spices should be harvested correctly and at the correct stage of maturity. The main obstacle
to correct harvesting is the crop being picked immature. This is usually due to fear of theft
or the farmer requiring money urgently.
Flowers such as ylang-ylang, should be picked very carefully and processed as soon as
possible.
The preparation of the material for distillation varies. Some materials, and in particular flowers,
should be distilled as quickly as possible. Many herbs are left to wilt, or are dried before
distillation while barks, seeds and roots can be dried and stored for several months prior to
distillation. Information on small scale drying systems can be found in the Practical Action
Technical Briefs on drying.
As oil is lost during drying care needs to be taken and low temperatures used. Allowing leaves to
dry in the shade or partial shade will result in less loss than direct sun drying. It is vital that the
material is dried to a moisture content that is low enough to prevent the growth of moulds and
typical moisture levels are shown in Table 2. The dried product should be stored in a cool place
and protected from any pick-up of moisture.
2