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 hop, Humulus Lupulus, Linne (N.O. Urticaceoe), is a scabrous climbing plant with perennial root, widely diffused over the whole of Europe and common in England, growing in hedges and thickets. It is largely cultivated in England, Germany, Russia,
The hop is dioecious, but the pistillate plant only is cultivated, since from that alone the fruits (hops) can be obtained; these are preferred with undeveloped seeds, to ensure which the staminate plants are usually excluded.
The fruit is a cone-like collective fruit (strobile) consisting of leafy stipules and bracts borne on a zigzag axis. These are picked from the plant when fully developed, and dried; they are frequently exposed to fumes of burning sulphur (sulphur dioxide), by which the colour is preserved and change in the aroma is said to be hindered. They are sometimes dried loose, but usually they are pressed into compact bales known as ' pockets.'
The strobile of the hop averages about 3.5 cm. in length and is ovoid or rounded in shape, the most conspicuous part being the yellowish green imbricated membranous bracts and stipules. If these leafy organs are removed from the strobile, the axis will be seen to be hairy and have a zigzag course, bearing rudimentary branches on alternate sides. Some of the leafy bodies enfold at their bases minute fruits: these are the bracts (fig. 72, b); others, the stipules, do not. The fruits are minute achenes, and are partially surrounded by a perianth (fig. 72, c). Both the minute fruits and the bases of the bracts are sprinkled over with yellowish shining translucent glands, which contain volatile oil and constitute, when separated, the drug lupulin.
The odour of fresh hops is strong and characteristic, although scarcely agreeable; the taste strongly aromatic and disagreeably bitter and acrid. By keeping, the aroma becomes less powerful but also less agreeable, the bracts and stipules turn yellow, and the glands acquire a brown colour.
The student should strip the bracts and stipules from the strobile and observe
(a) The zigzag hairy axis,
(b) The bracts enclosing fruits and bearing glands.
The composition of hops is very complex. They contain volatile oil, tannin, sugar, fatty acids, resins, etc. The volatile oil (0.3 to 1.0 per cent.) consists chiefly of the terpene humulene. The bitterness is due to a number of substances only one of which, humulol, has been obtained crystalline and pure. Some of these substances are soluble in water, others are constituents of the resin; xanthohumol is an orange yellow, crystalline body. One of the constituent resins yields by oxidation valerianic acid, a reaction that explains the change in the odour when hops are kept.
The volatile oil produces sedative and soporific effects, whilst the bitter substances are stomachic and tonic; hops accordingly improve the appetite and promote sleep.
Fig. 72. - Hop. a, strobile of the Hop, natural size, b, bract enfolding at its base a small fruit, and showing lupulin glands, natural size, c, fruit magnified, showing lupulin glands. (Tschirch).