Fresh oranges bought at the local supermarket are the legacy of a long history of cultivation which has given rise to countless hybrids of the orange tree, Citrus sinensis. The trees are cultivated in tropical regions worldwide. Enough varieties have been developed to warrant classification of this single species into 4 groups based on geographical ancestry and fruit characteristics. The groups are:
1. Mediterranean oranges
2. Spanish oranges
3. Blood oranges
4. Navel oranges
Most of the oranges currently being grown for production are Mediterranean and Spanish varieties. Blood oranges have dark red pulp and juice of excellent flavor. Navel oranges are a modern introduction especially appropriate for eating fresh because of their easy to peel skins and lack of seeds. Sweet orange oil can be extracted from any of these but is most often a by-product of Mediterranean and Spanish oranges grown for the juice industry. The oil found in the peel of the famous Valencia orange, a Spanish variety, is typical of the kind of sweet orange oil found on the market today.
The isolation of sweet orange oil and orange juice pose a challenge for producers. Unless the two are extracted cleanly and separately from each other, the quality of both will be diminished.
While most other essential oils are obtained by steam distillation of fresh plant material, citrus oils like sweet orange are adversely affected by that process. The acids in the fruit juice break down and diminish the citral content of the fresh oil when heat is applied. This results in a harsh aroma not at all resembling the freshly peeled fruit. Because distillation produces such a poor quality oil, the primary method of extracting sweet orange oil is through a physical process. Such oils are called "cold-pressed" because heat is not involved in the extraction and the peel is sometimes pressed to release the oil. This term is a bit misleading since the fruit is not cold but room temperature, and other means besides pressing are employed to release the oil from the glands in the peel of the orange.
The cold-pressing process is not without its own problems. The spongy white layer of the orange peel called "albedo" quickly absorbs any oil released from the thin, orange-colored outer layer known as "flavedo", thus decreasing the potential yield of essential oil. During its removal, the oil becomes bound up with wax particles and sticky pectin from the ruptured cells of the flavedo. It is very difficult to separate the oil from this semi-solid mixture once it forms, so processes like filtration and separation via centrifuge are required to obtain the clean, fresh oil.
It's important for aromatherapists to learn the differences between cold-pressed and distilled citrus oils. The changes in the constituent profiles caused by distillation make those oils much less therapeutically active than the cold-pressed versions. Cold-pressed oils smell like the fresh fruit, light and sweet. Distilled oils are sharp, bittersweet or powdery.
The difficulties associated with the extraction of sweet orange oil have engendered special techniques and equipment to do the job. Initially all oil was hand-pressed from the peel using a process called the "sponge method". This method was developed in Sicily and Calabria at least as early as 1776, according to written records. The fresh peels were squeezed by hand and the expressed oil was wiped away with a natural sea sponge. The sponging method solved all the problems associated with cold-pressed oils; it prevented the spongy albedo from absorbing the oil from the flavedo, and since the sponge absorbed and retained the pectin and waxes from the flavedo, the pure oil could be wrung from the sponge.
Although the sponge method yielded superior quality oil, the process was frustratingly slow, resulting in very costly oil.
The inefficiency of the sponge method gave rise to a wide array of devices in the early 20th century that processed oil from the separated peels of fruits by mechanical means. These machines, known as "sfumatrici", didn't actually press the peel but bent and rolled it, imitating the action of bending the peel back on itself between the thumb and forefingers and causing the oil to squirt out. The orange peels still had to be separated from the fruit by hand.
The next development in citrus oil extraction were devices known as "pellatrice" that processed oil from the whole fruit. Different types of pellatrice equipment are being used and refined today. Pellatrice separate the flavedo from the albedo with a grating or rasping action applied to the surface of the whole fruit. The released oil and flavedo particles are then refined through filtration and centrifuge. The remaining fruit, devoid of the flavedo, goes on to be processed for the juice it contains.
Anyone who's peeled a fresh orange will appreciate the refreshing, energizing, yet relaxing familiar aroma of good quality sweet orange oil. Sweet orange is the ideal wintertime aromatherapy oil. The aroma is sunny and refreshing but also warm and comforting. Blend orange with lemon or bergamot to heighten its refreshing and inspiring qualities. Or blend orange with neroli, lavender or jasmine to augment its relaxing and restful effects. A combination of spice oils such as cinnamon, clove or allspice will create a warm orange essence, ideal for diffusing with a candle lamp on cold winter evenings.
Sweet orange is a "fun" oil, especially liked by kids because of its sweet, recognizable fragrance. A balancing children's blend consisting of 66 drops orange and 34 drops of vanilla smells very much like orange tootsie pops!
However it's used, the quality of orange essential oil is key to its effectiveness. Hint: Learn the hallmarks of true cold-pressed orange oil by peeling different varieties of fresh, ripe orange fruit. Soon you will become a sweet orange connoisseur.