This section is from the book "Meals Medicinal", by W. T. Fernie. Also available from Amazon: Meals Medicinal: With "Herbal Simples" Curative Foods From the Cook in Place of Drugs From the Chemist.
(And See Milk).
The Kumys of the Kergese, who inhabit the Asiatic steppes - a fermented drink made from mare's milk, - was described by the father of history, Herodotus, and remains a typical Kergese product to this day. When the milk was drawn, it was poured into deep wooden vessels, and continually agitated for long hours by slaves whom the Scythians kept blind for this purpose. The upper part of the milk then became alcoholic in its solution, whilst the lower part remained as curdled casein, being more of a nutriment than an intoxicant. Mares' milk is not suitable for making butter, first, because it contains but little fat, and next because what fat can be got from it is not butter, but a half oily, lard-like substance of disagreeable taste. Even in the present day the nomads of the Russian steppes do not manufacture any butter, but they prepare large quantities of Kumys. From the above account it may be readily gathered that the artificial Koumiss of our modern dairies differs essentially from the true Koumiss of the Asiatic Kergese.
Koumiss, which consists, in its integrity, of mares' milk, fermented, is of particular value as a food for weakly, or consumptive patients, because of certain products generated from the milk sugar, which materially help a defective power of digestion. An imitation of the Russian Tartar Koumiss is now made with considerable success at our principal dairies, with cows' milk, sugar, and yeast. The original Koumiss was used by the Bashkirs of the steppes of Orenburg, and Ssamura, having been prepared by them from time immemorial as a restorative food, and a mild alcoholic drink, after the hardships and deprivations endured throughout a rigorous winter. It attracted the attention of the Russian physicians in 1830, and thirty years later, of the Germans; but mares' milk would be too laxative for ordinary use. Kephir is the modern substitute for Koumiss. It is a white, foaming, slightly sweet, acidulous, and alcoholic refreshing drink, the alcohol increasing until the whole of the sugar is used up, and a small amount of lactic acid being produced at the same time.
Kefyr grains, or fungi, are a ferment known to the hill folk of the Caucasus as acting on milk. Mares' milk contains but little fat, little casein, and much, lactose (or sugar of milk), of which constituents the proportions are just the reverse in cows' milk. In the production of genuine Koumiss, the vinous, and the lactic acid fermentations run side by side; three layers are produced in the bottles containing this Koumiss; the uppermost a little oil, the middle the vinous solution, and below some casein. Before use these are to be mixed by agitation. Home-made Koumiss may be prepared by mixing half a pint of water, half a pint of butter-milk, four pints of new milk, and one ounce of loaf sugar, leaving the mixture in a warm place, and shaking it occasionally for thirty-six hours. This will make a palatable form of nourishment, especially suitable for albuminuria from Bright's disease; likewise for the comparatively harmless albuminuria of adolescence, which is independent of any kidney trouble, but rather arising from defective digestion during growth; such latter illness yields readily to a strict milk diet, with rest in bed. The same beverage will generally overcome sleeplessness from imperfect digestion.
Its lactic acid is admirable for supplementing the gastric juice; and the state of vitality of the fermented Koumiss greatly assists the digestive processes.