The Story of Germ Life

by H. W. Conn

The object of the ripening of cream is to render it in a better condition for butter making. The butter maker has learned by long- experience that ripened cream churns more rapidly than sweet cream, and that he obtains a larger yield of butter therefrom. The great object of the ripening, however, is to develop in the butter the peculiar flavour and aroma which is characteristic of the highest product. Sweet cream butter lacks flavour and aroma, having indeed a taste almost identically the same as cream. Butter, however, that is made from ripened cream has a peculiar delicate flavour and aroma which is well known to lovers of butter, and which is developed during the ripening process.

Bacteriologists have been able to explain with a considerable degree of accuracy the object of this ripening. The process is really a fermentation comparable to the fermentation that takes place in a brewer's malt. The growth of bacteria during the ripening produces chemical changes of a somewhat complicated character, and concerns each of the ingredients of the milk. The lactic-acid organisms affect the milk sugar and produce lactic acid; others act upon the fat, producing slight changes therein; while others act upon the casein and the albumens of the milk. As a result, various biproducts of decomposition arise, and it is these biproducts of decomposition that make the difference between the ripened and the unripened cream. They render it sour and curdle it, and they also produce the flavours and aromas that characterize it. Products of decomposition are generally looked upon as undesirable for food, and this is equally true of these products that arise in cream if the decomposition is allowed to continue long enough. If the ripening, instead of being stopped at the end of a day or two, is allowed to continue several days, the cream becomes decayed and the butter made therefrom is decidedly offensive. But under the conditions of ordinary ripening, when the process is stopped at the right moment, the decomposition products are pleasant rather than unpleasant, and the flavours and aromas which they impart to the cream and to the subsequent butter are those that are desired. It is these decomposition products that give the peculiar character to a high quality of butter, and this peculiar quality is a matter that determines the price which the butter maker can obtain for his product.

But, unfortunately, the butter maker is not always able to depend upon the ripening. While commonly it progresses in a satisfactory manner, sometimes, for no reason that he can assign, the ripening does not progress normally. Instead of developing the pleasant aroma and flavour of the properly ripened cream, the cream develops unpleasant tastes. It may be bitter or somewhat tainted, and just as sure as these flavours develop in the cream, so sure does the quality of the butter suffer. Moreover, it has been learned by experience that some creameries are incapable of obtaining an equally good ripening of their cream. While some of them will obtain favourable results, others, with equal care, will obtain a far less favourable flavour and aroma in their butter. The reason for all this has been explained by modern bacteriology. In the milk, and consequently in the cream, there are always found many bacteria, but these are not always of the same kinds. There are scores, and probably hundreds, of species of bacteria common in and around our barns and dairies, and the bacteria that are abundant and that grow in different lots of cream will not be always the same. It makes a decided difference in the character of the ripening, and in the consequent flavours and aromas, whether one or another species of bacteria has been growing in the cream. Some species are found to produce good results with desired flavours, while others, under identical conditions, produce decidedly poor results with undesired flavours. If the butter maker obtains cream which is filled with a large number of bacteria capable of producing good flavours, then the ripening of his cream will be satisfactory and his butter will be of high quality. If, however, it chances that his cream contains only the species which produce unpleasant flavours, then the character of the ripening will be decidedly inferior and the butter will be of a poorer grade. Fortunately the majority of the kinds of bacteria liable to get into the cream from ordinary sources are such as produce either good effects upon the cream or do not materially influence the flavour or aroma. Hence it is that the ripening of cream will commonly produce good results. Bacteriologists have learned that there are some species of bacteria more or less common around our barns which produce undesirable effects upon flavour, and should these become especially abundant in the cream, then the character of the ripening and the quality of the subsequent butter will suffer. These malign species of bacteria, however, are not very common in properly kept barns and dairies. Hence the process that is so widely used, of simply allowing cream to ripen under the influence of any bacteria that happen to be in it, ordinarily produces good results. But our butter makers sometimes find, at the times when the cattle change from winter to summer or from summer to winter feed, that the ripening is abnormal. The reason appears to be that the cream has become infested with an abundance of malign species. The ripening that they produce is therefore an undesirable one, and the quality of the butter is sure to suffer.

So long as butter was made only in private dairies it was a matter of comparatively little importance if there was an occasional falling off in quality of this sort. When it was made a few pounds at a time, and only once or twice a week, it was not a very serious matter if a few churnings of butter did suffer in quality. But to-day the butter-making industries are becoming more and more concentrated into large creameries, and it is a matter of a good deal more importance to discover some means by which a uniformly high quality can be insured. If a creamery which makes five hundred pounds of butter per day suffers from such an injurious ripening, the quality of its butter will fall off to such an extent as to command a lower price, and the creamery suffers materially. Perhaps the continuation of such a trouble for two or three weeks would make a difference between financial success and failure in the creamery. With our concentration of the butter- making industries it is becoming thus desirable to discover some means of regulating this process more accurately.

The remedy of these occasional ill effects in cream ripening has not been within the reach of the butter maker. The butter maker must make butter with the cream that is furnished him, and if that cream is already impregnated with malign species of bacteria he is helpless. It is true that much can be done to remedy these difficulties by the exercise of especial care in the barns of the patrons of the creamery. If the barns, the cows, the dairies, the milk vessels, etc., are all kept in condition of strict cleanliness, if especial care is taken particularly at the seasons of the year when trouble is likely to arise, and if some attention is paid to the kind of food which the cattle eat, as a rule the cream will not become infected with injurious bacteria. It may be taken as a demonstrated fact that these malign bacteria come from sources of filth, and the careful avoidance of all such sources of filth will in a very large measure prevent their occurrence in the cream. Such measures as these have been found to be practicable in many creameries. Creameries which make the highest priced and the most uniform quality of butter are those in which the greatest care is taken in the barns and dairies to insure cleanliness and in the handling of the milk and cream. With such attention a large portion of the trouble which arises in the creameries from malign bacteria may be avoided.

But these methods furnish no sure remedy against evils of improper species of bacteria in cream ripening, and do not furnish any sure means of obtaining uniform flavour in butter. Even under the very best conditions the flavour of the butter will vary with the season of the year. Butter made in the winter is inferior to that made in the summer months; and while this is doubtless due in part to the different food which the cattle have and to the character of the cream resulting therefrom, these differences in the flavour of the butter are also in part dependent upon the different species of bacteria which are present in the ripening of cream at different seasons. The species of bacteria in June cream are different from those that are commonly present in January cream, and this is certainly a factor in determining the difference between winter and summer butter.

USE OF ARTIFICIAL BACTERIA CULTURES FOR CREAM RIPENING.

Bacteriologists have been for some time endeavouring to aid butter makers in this direction by furnishing them with the bacteria needful for the best results in cream ripening. The method of doing this is extremely simple in principle, but proves to be somewhat difficult in practice. It is only necessary to obtain the species of bacteria that produce the highest results, and then to furnish these in pure culture and in large quantity to the butter makers, to enable them to inoculate their cream with the species of bacteria which will produce the results that they desire. For this purpose bacteriologists have been for several years searching for the proper species of bacteria to produce the best results, and there have been put upon the market for sale several distinct "pure cultures" for this purpose. These have been obtained by different bacteriologists and dairymen in the northern European countries and also in the United States. These pure cultures are furnished to the dairymen in various forms, but they always consist of great quantities of certain kinds of bacteria which experience has found to be advantageous for the purpose of cream ripening.

There have hitherto appeared a number of difficulties in the way of reaching complete success in these directions. The most prominent arises in devising a method of using pure cultures in the creamery. The cream which the butter makers desire to ripen is, as we have seen, already impregnated with bacteria, and would ripen in a fashion of its own even if no pure culture of bacteria were added thereto. Pure cultures can not therefore be used as simply as can yeast in bread dough. It is plain that the simple addition of a pure culture to a mass of cream would not produce the desired effects, because the cream would be ripened then, not by the pure culture alone, but by the pure culture plus all of the bacteria that were originally present. It would, of course, be something of a question as to whether under these conditions the results would be favourable, and it would seem that this method would not furnish any means of getting rid of bad tastes and flavours which have come from the presence of malign species of bacteria. It is plainly desirable to get rid of the cream bacteria before the pure culture is added. This can be readily done by heating it to a temperature of 69 degrees C. (155 degrees F.) for a short time, this temperature being sufficient to destroy most of the bacteria. The subsequent addition of the pure culture of cream-ripening bacteria will cause the cream to ripen under the influence of the added culture alone. This method proves to be successful, and in the butter making countries in Europe it is becoming rapidly adopted.

In this country, however, this process has not as yet become very popular, inasmuch as the heating of the cream is a matter of considerable expense and trouble, and our butter makers have not been very ready to adopt it. For this reason, and also for the purpose of familiarizing butter makers with the use of pure cultures, it has been attempted to produce somewhat similar though less uniform results by the use of pure cultures in cream without previous healing. In the use of pure cultures in this way, the butter maker is directed to add to his cream a large amount of a prepared culture of certain species of bacteria, upon the principle that the addition of such a large number of bacteria to the cream, even though the cream is already inoculated with certain bacteria, will produce a ripening of the cream chiefly influenced by the artificially added culture. The culture thus added, being present in very much greater quantity than the other "wild" species, will have a much greater effect than any of them. This method, of course, cannot insure uniformity. While it may work satisfactorily in many cases, it is very evident that in others, when the cream is already filled with a large number of malign species of bacteria, such an artificial culture would not produce the desired results. This appears to be not only the theoretical but the actual experience. The addition of such pure cultures in many cases produces favourable results, but it does not always do so, and the result is not uniform. While the use of pure cultures in this way is an advantage over the method of simply allowing the cream to ripen normally without such additions, it is a method that is decidedly inferior to that which first pasteurizes the cream and subsequently adds a starter.