517. Koumiss.—Fermented mare milk has long been a favorite beverage in the East, where it is known as koumiss. In Europe and this country cow milk is employed in the manufacture of fermented milk, although it is less rich in lactose than mare milk. The process of manufacture is simple, provided a suitable starter is at hand. A portion of a previous brewing is the most convenient one, the fermentation being promoted by the addition of a little yeast. After the process of fermentation is finished the koumiss is placed in bottles and preserved in a horizontal position in a cellar, where the temperature is not allowed to rise above 12°.
518. Determination of Carbon Dioxid.—The carbon dioxid in koumiss is conveniently estimated by connecting the bottle by means of a champagne tap with a system of absorption bulbs.[529] The exit tube from the koumiss bottle passes first into an erlenmeyer, which serves to break and retain any bubbles that pass over. The water is next removed by means of sulfuric acid. The koumiss bottle is placed in a bath of water which is raised to the boiling point as the evolution of the gas is accomplished. The arrangement of the apparatus is shown in [Fig. 113]. At the end of the operation any residual carbon dioxid in the apparatus is removed by aspiration after removing the tap and connecting it with a soda-lime tube to hold the carbon dioxid in the air. A large balance suited to weighing the koumiss bottle is required for this determination. The carbon dioxid may also be determined, but less accurately, by loss of weight in the koumiss bottle after adding weight of water retained in the apparatus.
519. Acidity.—Although koumiss may contain a trace of acetic acid, it is best to determine the acid as lactic. The clarification is most easily accomplished by mixing the koumiss with an equal volume of ninety-five per cent alcohol, shaking and filtering. The first filtrate will usually be found clear. If not it is refiltered. In an aliquot part of the filtrate the acidity is determined by titration with tenth-normal sodium hydroxid solution, using phenolphthalein as indicator. The necessary corrections for dilution and volume of the precipitated casein are to be made. A linen filter may be used when paper is found too slow.
Fig. 113. Apparatus for Determining Carbon Dioxid in Koumiss.
520. Alcohol.—Half a liter of koumiss, to which 100 cubic centimeters of water have been added, is distilled until the distillate amounts to 500 cubic centimeters.
If the distillate be turbid 100 cubic centimeters of water are added and the distillation repeated. The alcohol is determined by the processes described hereafter.
521. Lactose.—The milk sugar may be determined by any of the methods described, but most conveniently by double dilution and polarization ([86]).
522. Fat.—Evaporate twenty grams of the sample to dryness and extract with pure ether or petroleum spirit in the manner already described ([455]).
The analysis is more quickly accomplished by the volumetric method of Babcock or Gerber ([473-475]).