Production—Lupulin is obtained by stripping off the bracts of hops, and shaking and rubbing them; and then separating the powder by a sieve. The powder thus detached ought to be washed by decantation, so as to remove from it the sand or earth with which it is always contaminated; finally it should be dried, and stored in well-closed bottles. From the dried strobiles, 8 to 12 per cent. of lupulin may be obtained.
Description—Lupulin seen in quantity appears as a yellowish-brown granular powder, having an agreeable odour of hops and a bitter aromatic taste. It is gradually wetted by water, instantly by alcohol or ether, but not by potash or sulphuric acid. By trituration in a mortar the cells are ruptured so that it may be worked into a plastic mass. Thrown into the air and then ignited, it burns with a brilliant flame like lycopodium.
Microscopic Structure—The lupulinic gland or grain, like the generality of analogous organs, is formed by an intumescence of the cuticle of the nuculæ and bracts of hop ([see p. 552]). Each grain is originally attached by a very short stalk, which is no longer perceptible in the drug. The gland, exhausted by ether and macerated in water, is a globular or ovoid thin-walled sac, measuring from 140 to 240 mkm. It consists of two distinct, nearly hemispherical parts; that originally provided with the stalk is built up of tabular polyhedric cells, whilst the upper hemisphere shows a continuous delicate membrane. This part therefore easily collapses, and thus exhibits a variety of form, the greater also as the grains turn pole or equator to the observer.[2062]
The hop gland is filled with a thick, dark brown or yellowish liquid, which in the drug is contracted into one mass occupying the centre of the gland. It may be expelled in minute drops when the wall is made to burst by warming the grain in glycerin. The colouring matter, to which the wall owes its fine yellow colour, adheres more obstinately to the thinner hemisphere, and is more easily extracted from the thicker part by means of ether.
Chemical Composition—The odour of lupulinic grains resides in the essential oil, described in the previous article. The bitter principle formerly called Lupulin or Lupulite was first isolated by Lermer (1863) who called it the bitter acid of hops (Hopfenbittersäure). It crystallizes in large brittle rhombic prisms, and possesses in a high degree the peculiar bitter taste of beer, in which however it can be present only in very small proportion, it being nearly insoluble in water, though easily dissolved by many other liquids. The composition of this acid, C₃₂H₅₀O₇, appears to approximate it to absinthiin; it is contained in the glands in but small proportion. Still smaller is the amount of another crystallizable constituent, regarded by Lermer as an alkaloid.
The main contents of the hop gland consist of wax (Myricylic palmitate, according to Lermer), and resins, one of which is crystalline and unites with bases.
A good specimen of German lupulin, dried over sulphuric acid, yielded us 7·3 per cent. of ash. The same drug exhausted by boiling ether, afforded 76·8 per cent. of an extremely aromatic extract, which on exposure to the steam-bath for a week, lost 3·03 per cent., this loss corresponding to the volatile oil and acids. The residual part was soluble in glacial acetic acid and could therefore contain but very little fatty matter.
Uses—The drug has the properties of hops, but with less of astringency. It is not often prescribed.
Adulteration—Lupulin is apt to contain sand, and on incineration often leaves a large amount of ash. Other extraneous matters which are not unfrequent may be easily recognized by means of a lens. As the essential oil in lupulin is soon resinified, the latter should be preferred fresh, and should be kept excluded from the air.