This is the most widely used industrial method for the isolation of essential oil from plant material. Here the steam is produced outside the still, usually in a steam boiler. Steam at optimum pressure is introduced into the still below the charge through a perforated coil or jets. Steam distillation is relatively rapid and is capable of greater control by the operator. The steam pressure inside the still could be progressively increased as distillation proceeds for complete recovery of high-boiling constituents. The still can be emptied and recharged quickly. With the immediate reintroduction of steam, there is no unnecessary delay in the commencement of the distillation process. Oils produced by this method are of more acceptable quality than those produced by the other methods.
Ginger oil is commercially produced by steam distillation of the comminuted dried spice. The spice is powdered and charged in a stainless steel still of optimum dimensions. The still is attached to a heat exchanger (condenser) and a separator. Direct steam is admitted from the bottom of the still. The steam, which rises through the charge, carries along with it the vapors of the volatile oil. The oil vapor-steam mixture is cooled in the condenser. The oil is separated from water in the separator and collected in glass or stainless steel bottles. The oil is thoroughly dried and stored airtight in full containers in a cool dry place protected from light. A schematic layout of a steam distillation assembly is given in Figure 11.1.
The volatile oil derived from dried ginger is a free-flowing, pale greenish yellow liquid possessing the characteristic aroma but not the pungent taste (bite) of the spice. Ginger oil is soluble in ether and insoluble in water. The odor of the oil is quite lasting.
Physical properties such as specific gravity, refractive index, and optical (angular) rotation serve as yardsticks for the primary qualification of ginger oil. Food Chemicals Codex (FCC) specifications for ginger oil (FCC, 1996) are given in Table 11.17.
Table 11.17 FCC Specifications for Ginger Oil
Angular rotation Heavy metals (as Pb) Refractive index Saponification value Specific gravity
Between 1.488 and 1.494 at 20°C
Not more than 20
Between 0.870 and 0.882 at 25°C
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You have probably heard the term Aromatherapy and wondered what exactly that funny word, „aromatherapy‟ actually means. It is the use of plant oils in there most essential form to promote both mental and physical well being. The use of the word aroma implies the process of inhaling the scents from these oils into your lungs for therapeutic benefit.