A Milk Filling Apparatus
Fig. 10—Where soured milk is handled on the large scale, a special filling apparatus for bottles is desirable, and the soured milk supply should be under cover as shown. This apparatus is made by the Dairy Machinery and Construction Company.
Krannhals[52] succeeded in isolating ten different keffir bacteria among which were several sporulating bacteria. Here too it is impossible to attach any importance to the results, as the artificial preparation of keffir, by means of these bacteria, was not attempted. Beijerinck[53] studied the organisms constituting keffir grains and attached prime importance to the occurrence of two organisms, viz., (a) a yeast, Saccharomyces kefir, which was capable of inverting milk sugar by means of an enzyme (lactase) and afterwards fermented the products with the formation of alcohol and carbon dioxide, and also (b) a non-motile non-sporulating bacterium, afterwards Lactobac. caucasicus. The latter, when cultivated on gelatine, gave rise to tough warty colonies about 1/40 in. diameter, and was regarded as one of the lactic acid bacteria found in milk which has been incubated at 77° to 90° F. and afterwards incubated at a higher temperature, 100° to 104° F. Scholl[54] isolated three different organisms, of which a yeast inverted milk sugar for the lactic acid bacteria, while Dispora peptonised the albuminoid matters.
Adametz[55] failed to isolate Dispora, and came to the conclusion that ordinary lactic bacteria and yeasts played the most important part in the fermentation.
Essaulow found in keffir grains six different organisms—yeast cells, cocci, short thick bacilli, bent bacilli, long threads, and motile bacteria. The two latter would seem to be Bacillus subtilis, while the others may be regarded as Bacterium acidi lactici (Hueppe), Bacterium aërogenes, and Streptococcus lacticus (Grotenfeldt). Pure cultures were insufficient to produce keffir, while mixed cultures of Bacterium acidi lactici and yeasts were effective.
Freudenreich,[56] to whom we owe a record of very carefully executed experiments, could not arrive at a satisfactory explanation of the rôle of Bacillus caucasicus. This organism is described as being 5-6 µ long and 1 µ thick, slightly motile, and possessing bright refractive spots at the poles of the bacilli. It is extremely difficult to cultivate, and forms flat, small greyish colonies of irregular outline. The bright refractive spots above referred to are, however, granules taking the usual stains quite readily, and not spores as supposed by Kern.
Freudenreich also found three other organisms—a yeast and two streptococci. The yeast, to which he gave the name Saccharomyces (Torula) keffir, forms small oval or roundish cells 2-3 µ wide and 3-5 µ long. The optimum temperature would seem to be about 72° F.; the maximum 82° F. This organism is unable to ferment milk directly, but is able to decompose maltose and glucose with gas production. It does not coagulate milk, but imparts to it a characteristic taste and is unable to withstand desiccation for more than a few days.
Of the two streptococci isolated, Streptococcus a resembles organisms of the group Streptococcus lacticus in appearance, but is able to ferment milk, with weak acid and gas production, and is capable of inducing coagulation.