Outlines of dairy bacteriology, 10th edition / A concise manual for the use of students in dairying

by H. L. Russell; E. G. Hastings

When the starter is propagated under practical conditions, it sooner or later deteriorates, either in acid production, or in flavor, and a new pure culture must be procured from the manufacturer. It is impossible to give a hard and fast rule as to the length of time a starter can be kept in good condition. It will depend on how well the maker satisfies the conditions necessary for maintaining its purity and strength. The use of imperfectly sterilized milk, or dirty utensils soon contaminates it; overripening is likely to injure the flavor. One of the most frequent troubles encountered is the appearance of a slimy or ropy condition in the starter, although the acidity developed may be normal and the flavor desirable. It has been found that this condition is not necessarily due to contamination, as was considered true in the past, but rather to some change in the lactic bacteria themselves. If the propagation is continued, the slimy condition will often disappear.

Starters in "process" butter and oleomargarine. The advance which has recently been made in the science and practice of cream ripening and butter production is utilized most effectively in the treatment of cream in the renovating process. Old, soured, and stale cream is reduced in acidity by the addition of lime. The cream is then pasteurized and aerated to expel the odors as much as possible. A large amount of starter is then added and the cream immediately churned. Under these conditions, the bad flavors are materially reduced in intensity, and desirable flavors absorbed by the fat from the selected starter used. It is thus possible to produce butter of good quality from cream that would at first be regarded as quite unsuitable for butter production.

In the manufacture of oleomargarine the same principle is utilized. The butter aroma and flavor is imparted to the neutral oils and tasteless fats by mixing the same with a properly prepared starter. Renovated or process butter is given a desirable flavor in the same way.

Wash water. It has been found that the purity of the water used in washing the granular butter has a marked influence on the keeping quality. If the water is from a shallow well into which surface water finds its way, it is certain to contain large numbers of those types of bacteria that are found in the soil, while if it comes from a deep well that is properly protected from surface contamination, the bacterial content of the water will be low and no injurious effect on the butter will be noted. When it is impossible to obtain pure water for washing purposes, a proper supply may be secured by sterilizing the water. The most convenient way of heating the water is by the direct injection of steam. It is necessary to use that coming directly from the boilers and not the exhaust from the engine, since the latter is likely to contain small amounts of oil that will impart to the butter an objectionable flavor. After cooling, the water is ready for use. It has been shown that the cost of treating an impure water is more than covered by the increased returns from the product.

A pure and healthful water supply should be one of the essential things of every dairy, creamery, and cheese factory, not only for the sake of the quality of the product, but also to avoid contamination of products with disease-producing bacteria.

Bacteria in butter. The germ content of butter will depend on the type of cream. Sweet-cream butter contains but few bacteria. In sour-cream butter the content in bacteria will be greatly increased, especially as to lactic organisms. Often, it may amount to several millions of organisms per gram. The germ content of butter is said to be greater on the outside of a package than within the mass, due doubtless to the free access of air, thus favoring the growth of the aerobic forms.

The composition of normal butter does not favor the growth of the majority of kinds of bacteria that are contained in it. The washing process removes much of the material suitable as food for the bacteria, such as sugar and albumen. If considerable butter milk is left in the butter, the growth of bacteria will be quite rapid, at first, but does not continue for any considerable length of time. The addition of salt also tends to restrain the growth of most kinds of bacteria.

Butter is at its best when it is perfectly fresh. Deterioration begins within a short time and the rapidity with which the changes go on is dependent on the temperature at which the butter is stored. The temperature of the butter rooms in the large cold storage plants is kept below 0° F. The butter in such rooms will deteriorate very slowly, but on removal from the cold rooms and in storage at ordinary temperatures deterioration goes on more rapidly than would have been the case when the butter was fresh. At the temperature of an ordinary refrigerator the changes go on much more rapidly. This fact has often been looked on as indicating that the factors causing the changes are biological ones. The influence of temperature in accelerating the changes would be the same if no biological factor were active.

That biological factors are of importance is indicated by the fact that the keeping quality of the product is profoundly affected by the quality of the cream. Butter made from sweet, fresh cream, that has been thoroughly pasteurized, has the best keeping quality, while butter made from such cream, but not pasteurized, has the poorest keeping quality, especially when no salt is added. Every process by which the desirable lactic bacteria are increased in proportion to other kinds has a marked effect in enhancing the keeping quality of the butter. Thus, the use of pure cultures in raw cream, and pasteurization together with the pure cultures, have a marked beneficial effect.

The addition of preservatives exerts an effect on keeping quality. Borax is the chemical most frequently employed for this purpose. Its use is allowed in Australia and New Zealand in butter that is shipped to England, but the use of all preservatives is forbidden in the United States.