Changes perceived in milk and its products, therefore also in cheeses, usually take place under the influence of various microorganisms. We can sometimes influence these transformations of a fermentative nature, and even guide them. Yes in buttering, where, in fact, it is only about one fermentation, i.e.. to sour cream, pasteurizing her, we can achieve flawless conversion of lactic sugar to lactic acid by means of a leaven from one or more species of beneficial bacteria. It is not so simple in cheese making. The difficulties that arise here stem from this, that various fermentation changes take place in the cheeses, little explored yet, containing many factors, on which a favorable or unfavorable final result depends, that is, the production of correct or defective cheese. In this section, we encounter this inconvenience at the very beginning of the modification, that we cannot always use milk pasteurization, since many types of pasteurized milk cheeses do not achieve their full advantages over cheeses, for which raw milk was used. Whether you like it or not, we transplant a mixture of all these microorganisms into the cheese from raw milk, so useful, as well as harmful or passive, which accidentally found themselves in it, starting with milking. Now you should know or at least feel their character, quantity, which of them have an advantage, how they live and work, that we need, which to support, and which to combat and how.
Milk produced in a healthy organism is almost free from microorganisms and would have an unlimited shelf life, if it did not then become infected. But bacteria are already present in the milky bay of the udder, which got there through the Strzykowy canal nipples. So milk from the first teats contains a lot of them. Then it becomes infected with more or less microorganisms from the environment, which mainly depends on the degree of neatness observed during milking and the method of storage.
When bacteria get into milk, they find favorable conditions for life and development in it, i.e.. complete food and a favorable temperature, because around 35 ° C, when the milk does not cool down. Therefore they develop with dizzying speed. Admittedly, fresh milk initially defends itself against microbial attacks (bactericidal properties), but only for a few hours. Initially, the activity of the bacteria is poorly manifested, because they use a lot of energy to reproduce, and only later do their enzymes become active. The milk succumbs to the invaders, it changes more and more.
Not all milk has the same fermentability. In practice it says, that it is more or less capable, or even inappropriate. The symptom is like this, that from the very beginning the desired fermentation in the different milk develops either properly, or reluctantly, the same is true for the cheese-making period. Individual cows in the same barn, equally fed, they give milk of different fermentability, what you should pay attention to when choosing milk intended for sourdough. This symptom is probably related to the chemistry of milk formation in the animal's body.
About milk, the so-called. dysgenetycznym, that is, paralyzing the growth of some bacteria will be mentioned in the description of milk defects.
Under normal conditions, microorganisms active in milk and milk products are divided according to the chemical transformations they make and morphological features into the following groups: lactobacilli, propionic acid bacteria, protein breakdown bacteria, butyric acid bacteria, yeasts and molds.
The basis for the implementation of proper cheese maturation from the very beginning of its course is the transformation of milk sugar into pure lactic acid. Depending on this regulator, other changes in cheese remain, made by various microorganisms on the acidic medium prepared in this way.