The concept of Aromatherapy is primarily based on the use of aromatic herbs (those which give out a scent, a perfume or an aroma). It is therefore an intrinsic part of herbal medicine (or Phytotherapy as it is called in Europe). If the herb is aromatic, i.e. it liberates a scent, a perfume or an aroma, it's Aromatherapy. Drinking a tea made up of thyme or rosemary, is in fact practicing Aromatherapy. Since the aroma of the herb is dependent on the presence of essential oils, Aromatherapy has been progressively related to these elements. Essential oils are lipid soluble phyto-chemicals present in more or less concentrations within the plant itself. In order to be available, they have to be extracted. Several methods of extraction are performed today. Each method is dependent on the industry it is related to and on the type of plant used. Essential oils extracted from the peel of fruits are using a method called expression, where the peel is mechanically expressed in order to force out the substance. This can be done manually or industrially. The most ancient and still common method is steam distillation where the herb is submitted to low pressure steam which volatilizes the aromatic substances out of the plant and deposit them along with the water after condensation. The water soluble elements are diluted in the water which becomes aromatic, hence known as the hydrolate, whereas the lipid soluble elements float on the surface, they are known as the essential oils. Other extraction processes involve the use of solvents. Modern techniques rely on CO2 extractions. In medical Aromatherapy, the preferred method of extraction is steam distillation at low speed, low temperature and low pressure.Such extractions yield pharmaceutical quality essential oils and hydrolates.