Outlines of Dairy Bacteriology, 8th edition / A Concise Manual for the Use of Students in Dairying

by H. L. Russell

A very satisfactory way in which these cultures are marketed is to mix the bacterial growth with some sterile, inert, dry substance. This is the method used in most of the Danish cultures. In this country, some of the more prominent cultures employed are marketed in a liquid form.

Culture vs. home-made starters. One great advantage which has accrued from the use of culture or commercial starters has been that in emphasizing the need of closer control of the ripening process, greater attention has been paid to the carrying out of the details. In the hands of the better operators, the differences in flavor of butter made with a culture or a natural starter are not marked,[168] but in the hands of those who fail to make a good product under ordinary conditions, an improvement is often secured where a commercial culture is used.

Pasteurization as applied to butter-making. This process, as applied to butter making, is often confounded with the treatment of milk and cream for direct consumption. It is unfortunate that the same term is used in connection with the two methods, for they have but little in common except in the use of heat to destroy the germ life of the milk. In pasteurizing cream for butter-making, it is not necessary to observe the stringent precautions that are to be noted in the preservation of milk; for the addition of a rapidly developing starter controls at once the fermentative changes that subsequently occur. Then again, the physical requirement as to the production of a cooked taste is not so stringent in butter-making. While a cooked taste is imparted to milk or even cream at about 158° F., it is possible to make butter that shows no permanent cooked taste from cream that has been raised as high as 185° or even 195° F. This is due to the fact that the fat does not readily take up those substances that give to scalded milk its peculiar flavor.

Unless care is taken in the manipulation of the heated cream, the grain or body of the butter may be injured. This tendency can be overcome if the ripened cream is chilled to 48° F. for about two hours before churning. It is also essential that the heated cream should be quickly and thoroughly chilled after being pasteurized.

The Danes, who were the first to employ pasteurization in butter-making, used, in the beginning, a temperature ranging from 158° to 167° F., but owing to the prevalence of such diseases as tuberculosis and foot-and-mouth disease, it became necessary to treat all of the skim milk that was returned from the creameries. For this purpose the skim milk is heated to a temperature of 176° F., it having been more recently determined that this degree of heat is sufficient to destroy the seeds of disease. With the use of this higher temperature the capacity of the pasteurizing apparatus is considerably reduced, but the higher temperature is rendered necessary by the prevailing conditions as to disease.

When the system was first introduced in Denmark, two methods of procedure were followed: the whole milk was heated to a sufficiently high temperature to thoroughly pasteurize it before it was separated, or it was separated first, and the cream pasteurized afterwards. In the latter case, it is necessary to heat the skim milk after separation to destroy the disease organisms, but this can be quickly done by the use of steam directly. Much more care must be used in heating the cream in order to prevent injury to the grain of the butter. In spite of the extra trouble of heating the cream and skim milk separately, this method has practically supplanted the single heating. With the continual spread of tuberculosis in America the heating of skim milk separately is beginning to be introduced.[169]

Use of starters in pasteurized and unpasteurized cream. In order to secure the beneficial results presumably attributable to the use of a starter, natural as well as a pure culture, it should be employed in cream in which the bacteria have first been killed out by pasteurization. This is certainly the most logical and scientific method and is the way in which the process has been developed in Denmark.

Here in this country, the use of pure cultures has been quite rapidly extended, but the system of heating the cream has been used in only a slight measure. The increased labor and expense incurred in pasteurizing the cream has naturally militated somewhat against the wide-spread use of the process, but doubtless the main factor has been the inability to secure as high a flavor where the cream was heated as in the unheated product. As the demands of the market change from a high, quick flavor to one that is somewhat milder but of better keeping quality, doubtless pasteurization of the cream will become more and more popular. That such a change is gradually occurring is already evident, although as yet only a small proportion of butter made in this country is now made in this way. Where the cream is unheated, a considerable number of species will be found, and even the addition of a pure culture, if that culture is of the lactic acid-producing species, will to some extent control the type of fermentation that occurs. Such would not be the case with a culture composed of the casein-digesting type of bacteria. Only those forms could thus be used which are especially well suited to development in raw cream. For this reason the pure culture ferments that are generally employed in creamery practice are organisms of the lactic acid type, able to grow rapidly in cream and produce a pure cream flavor in the butter.

Purity of commercial starters. Naturally the butter maker is forced to rely on the laboratory for his commercial starter, and the question will often arise as to the purity and vigor of the various ferments employed. As there is no way for the factory operator to ascertain the actual condition of the starter, except by using the same, the greatest care should be taken by the manufacturer to insure the absolute purity of the seed used.