AMPELIDEÆ.
UVÆ PASSÆ.
Passulæ majores; Raisins; F. Raisins; G. Rosinen.
Botanical Origin—Vitis vinifera L., the Common Grape-vine. It appears to be indigenous to the Caucasian provinces of Russia, that is to say, to the country lying between the eastern end of the Black Sea and the south-western shores of the Caspian; extending thence southward into Armenia. Under innumerable varieties, it is cultivated in most of the warmer and drier countries of the temperate regions of both the northern and southern hemispheres. Humboldt defines the area of the profitable culture of the vine as a zone lying between 36° and 40° of north latitude.
History—The vine is among the oldest of cultivated plants, and is mentioned in the earliest Mosaic writings. Dried grapes as distinguished from fresh were used by the ancient Hebrews, and in the Vulgate are translated Uvæ passæ.[647] During the middle ages, raisins were an article of luxury imported into England from Spain.
Description—The ovary of Vitis vinifera is 2-celled with 2 ovules in each cell; it develops into a succulent, pedicellate berry of spherical or ovoid form, in which the cells are obliterated and some of the seeds generally abortive. As the fruit is not articulated with the rachis or the rachis with the branch, it does not drop at maturity but remains attached to the plant, on which, provided there is sufficient solar heat, it gradually withers and dries: such fruits are called Raisins of the sun. Various methods are adopted to facilitate the drying of the fruit, such as dipping the bunches in boiling water or in a lye of wood ashes, or twisting or partially severing the stalk,—the effect of each operation being to arrest or destroy the vitality of the tissues. The drying is performed by exposure to the sun, sometimes supplemented by artificial heat.
The raisins commonly found in the shops are the produce of Spain and Asia Minor, and are sold either in entire bunches or removed from the stalk. The former kind, known as Muscatel Raisins and imported from Malaga, are dried and packed with great care for use as a dessert fruit. The latter kind, which includes the Valencia Raisins of Spain, and the Eleme, Chesme and stoneless Sultana Raisins of Smyrna, are used for culinary purposes. For pharmacy, Valencia raisins are generally employed.
Microscopic Structure—The outer layer or skin of the berry is made up of small tabular cells loaded with a reddish granular matter, which on addition of an alcoholic solution of perchloride of iron assumes a dingy green hue. The interior parenchyme exhibits large, thin-walled, loose cells containing an abundance of crystals (bitartrate of potassium and sugar). There are also some fibro-vascular bundles traversing the tissue in no regular order.
Chemical Composition—The pulp abounds in grape sugar and cream of tartar, each of which in old raisins may be found crystallized in nodular masses; it also contains gum and malic acid. The seeds afford 15 to 18 per cent. of a bland fixed oil, which is occasionally extracted. Fitz[648] has shown that it consists of the glycerides of Erucic Acid, C₂₂H₄₂O₂, stearic acid, and palmitic acid, the first-named acid largely prevailing. The crystals of erucic acid melt at 34° C.; by means of fused potash they may be resolved into arachic acid, C₂₀H₄₀O₂, and acetic acid, C₂H₄O₂.
The seeds further contain 5 to 6 per cent. of tannic acid, which also exists in the skin of the fruit. The latter is likewise the seat of chlorophyll and other colouring matter.