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. 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. 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.