During any interruption in the preparation of keffir in the above manner, the grains are taken out, and after having been well washed in clean water, are spread out on a clean cloth to dry in the sunshine. They thereby assume a characteristic cheesy or buttery odour and become rather darker in colour. Thorough desiccation is essential in order to prevent subsequent mouldiness or disease of the grain.
In European countries the grains are subjected to a preliminary soaking in water for five to six hours and then placed in four to five changes of milk, each change having a duration of two to three hours. As soon as the grains commence to rise to the surface of the milk, they may be used for the actual preparation. To this end, a small quantity of the grain is added to freshly boiled milk and allowed to stand for eight to twelve hours at a temperature of 55°-62° F. with agitation of the flask every two hours. By this time the milk, now known as Sakwaska, has become abundantly inoculated with the organisms essential to the fermentation, and after the removal of the grains, may be poured into well-corked flasks for the secondary brew. The flasks should be kept at a lower temperature for twenty-four to forty-eight hours, by which time the product is ready for consumption.
According to the temperature and length of period to which this subsequent fermentation is allowed to proceed, the resultant keffir is more or less acid and gaseous. The grains may again be used for starting a fresh portion of milk, and a regular supply obtained in this manner. Well-fermented forty-eight-hours-old keffir should be an effervescent beverage with prickling and acid taste and a consistency and smell similar to sour cream. Large, persistent bubbles should form on the surface of the liquid and the casein be present as an extremely fine flocculent precipitate which remains suspended for a considerable time.
From the third day there ensues a gradual peptonisation of the casein. If the temperature at which the secondary fermentation has occurred should be higher than 72° F., or if the milk has not been sufficiently agitated, then the casein will be present in the form of porous small flakes, which on shaking form a fine emulsion.
The chemical changes undergone by the milk during the preparation of keffir are confined almost exclusively to the milk sugar. As already stated, a slight peptonisation occurs in old samples, but this depends very largely upon the method of preparation and purity of the culture. Hammersten[49] and Essaulow[50] show, however, that this is not a concomitant of normal fermentation. According to Hammersten, normal keffir contains—
| Per cent. | |
| Water | 88.26 |
| Fat | 3.35 |
| Casein | 2.98 |
| Lactalbumen | 0.28 |
| Peptones | 0.05 |
| Milk sugar | 2.78 |
| Lactic acid | 0.81 |
| Alcohol | 0.70 |
| Ash | 0.79 |
In no case should the acid be higher than 1.0 per cent., and the alcohol more than 0.75 per cent.
Biology of the Keffir Grain.—The first communication on the biology of the keffir grain seems to have been made by Kern.[51] He regarded the grain as a zoöglœa composed of bacilli and yeasts, the latter being regarded as the ordinary beer yeast (Saccharomyces cerevisseæ), while to the former he gave the name of Dispora caucasica. As the name indicates, this bacillus possesses two polar spores, and germination of these proceeded in the same manner as with Bac. subtilis. As, however, pure cultures of the organisms were not made, and the descriptions and illustrations made by Kern fail to show any distinctive characteristics, it seems probable that accidental confusion with other organisms must have occurred.