This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The vanilla plant, Vanilla plantfolia, Andrews (N.O. Orchideoe), is a climbing plant growing wild in the moist woods on the eastern coast of Mexico. It is now largely cultivated in the islands Reunion, the Seychelles, Mauritius, Tahiti, Java, etc, where the climate resembles in temperature and humidity that of its native country. The genus includes many species, but V. planifolia is the chief vanilla-yielding one.
Like other members of the same natural order, the fertilisation of the Mexican wild plant is effected by insects; but when the plant is cultivated in other countries, in the absence of these insects, the fertilisation is accomplished by hand. This is effected by introducing a pointed stick into flower after flower, selecting the strongest. Before the fruits ripen, when the colour begins to change from yellowish green to brown, they are picked and subjected to a process of ' curing,' during which certain aromatic principles are formed and the fruits acquire the well-known vanilla odour. This process, the details of which vary considerably, consists essentially in slowly drying the fruits by exposure to the warmth of the sun or to artificial heat. The change in the constituents is probably due to the action of enzymes of which two, a hydrolysing enzyme and an oxydase have been detected, but the exact nature of the change or of the substances acted upon is not known. The cured fruits, which are of a dark brown or nearly black colour, are bound in bundles and packed in tins, in which they gradually become coated with minute crystals.
Commercial vanilla occurs in slender flexible sticklike pods about 15 to 20 cm. in length, and of a dark brown or nearly black colour. They have a flattened-cylindrical shape, due to the mutual pressure of the pods in the bundle, and taper towards both base and apex. The surface is longitudinally wrinkled and frequently more or less covered with numerous minute glistening crystals (of vanillin). The fruits are one-celled and contain innumerable, minute, black seeds embedded in a dark-coloured, aromatic, balsamic fluid secreted by the cells of the inner epidermis of the pericarp, which are developed into short hair-like processes projecting into the cavity of the fruit. The drug has an extremely fragrant odour and an agreeable aromatic taste.
Fig. 78. - Vanilla. Transverse section of fruit, showing the placentas, seeds, and secreting hairs on inner epidermis of the pericarp. Magnified. (Moeller).
The principal aromatic constituent of vanilla pods is vanillin, though probably other aromatic substances are present; it is contained in the fluid secreted by the inner epidermis of the pericarp, which gradually permeates the whole fruit, and constitutes the crystalline deposit that slowly accumulates on the pods.
Vanillin, the aldehyde of methylprotocatechuic acid, can be obtained in colourless acicular crystals with a fragrant vanilla-like odour. It also occurs in balsam of Peru, balsam of Tolu, benzoin, and other drugs; it is now prepared in large quantities from eugenol, the principal constituent of clove oil.