Rubinsky states that, among the nomadic tribe, of Khirgiz and Kalmucks, a special leathern bottle (Turssuk, Orroth, or Soaba) is used for the preparation of koumiss, while wooden tubs (Tschiljak) similar in shape to the old-fashioned churn are used by the Bashkirs, and in koumiss establishments. The fermentation is induced by the addition of koumiss to fresh mares' milk, in proportions which vary according to the cleanliness observed in the actual preparation. Where the process is carefully controlled, one part of koumiss to ten parts of milk is often used, but where gross infection from outside sources takes place one part of koumiss to three parts of milk is taken. The mixture is stirred at frequent intervals, and stored at a temperature of 73°-90° F. Weak koumiss is obtained after twenty to twenty-four hours in winter and twelve to fourteen hours in summer, but is scarcely ever consumed immediately, as it possesses a strong purgative action. It is generally poured into bottles (bottled koumiss); or allowed to remain in the tubs (tschiljak koumiss); in the former case the fermentation is anaërobic, in the second it is aërobic. Storage of the koumiss upon ice or in a cellar is necessary since medium koumiss is converted to strong koumiss in twelve to sixteen hours at ordinary temperatures, while at the lower temperature this occurs only in two to four days.[60] According to Biel,[61] either old koumiss or the dried sediment from old koumiss may be used for the initial inoculation. It may also be prepared by the repeated inoculation of mares' milk with soured cows' milk until a fermenting product is obtained. Koumiss may be prepared by a method stated by Allik[62] to be in general use in the Caucasian health-resorts. One part of beer-yeast is added to four to ten parts of fresh mares' milk (according to the strength of product required), and after thorough mixture of the two liquids the whole is allowed to ferment at a temperature of 70° to 72° F. for two days. One part of this first product is then added to five parts of fresh cold milk, and allowed to stand three to four hours at 75° to 77° F. It is then poured into bottles, and after the expiration of another three to four hours is stored away in a cellar at about 45° F. This koumiss may be used at any time from one to five days (generally two to three) after bottling according to the strength desired or prescribed in each individual case. The changes undergone during fermentation consist in a vigorous gas and acid production accompanied by alcohol formation and coagulation of the milk. The coagulum exists in an extremely fine state of division, and the liquid froths violently on the bottle being opened. It has a full pleasant acid taste, but should not contain more than one per cent. acid and two per cent. alcohol. The specific gravity of koumiss is 1.008 to 1.020 at 60° F. Appended is an analysis of two different samples of koumiss: