One of the most important practical trials in cheese making is the fermentation test, which to some extent allows to easily assess the suitability of milk for processing by indicating, which microorganisms have an advantage in milk and what will be the approximate course of cheese fermentation. Although its results are known only after the lapse of time 24 hours, so actually too late, because after processing the milk, after all, its value lies in this, that it warns against the delivery of defective milk in the future and indicates who is delivering it. Knowing the source of the defect makes it easier to deal with it. Performing the fermentation test is easy and does not require expensive equipment.
For test tubes with a diameter of approx 20 mm, heights 180 mm and calibrated to capacity 40 cm3, carefully sterilized (preferably with alcohol or hot water and baking soda) pours in 40 cm3 of milk, then put them on 24 hours until the fermentation apparatus, in which the temperature is kept constantly 38 do 40°C. That is why it is so important to maintain this temperature, because it promotes the growth of harmful bacteria, primarily bloating cola and aerogenes.
In addition, good milk may appear to be defective at higher temperatures, and in the lower one - defective can be considered good. It is necessary for the validity of the assessment, that all tubes have the same diameter. Nevertheless, evaluation requires practice due to the numerous intermediate thrombotic types.
I. Evaluation after 12 hours. Healthy milk should remain liquid, have clean, at most a pleasant sour smell or showing only traces of clotting. Such changes can be seen in defective milk beforehand, which usually take place after 24 hours, and which we will learn below. Only at this time coagulated milk in the form of pure, not scratched jelly should be assessed more leniently. It is sour milk under the influence of ordinary lactic acid bacteria. They can be described as impermanent, but not as defective.
yl. Evaluation after 24 hours. After 24 For hours, healthy milk containing predominantly beneficial lactic acid bacteria should form a smooth, uniform clot. But we usually get a variety of clots, which A. Peter can be classified into four main types: gl (gelatinous), s (caseous), With (grainy) i w (bloating).
In addition to the clotted types, there is also the liquid type. Each one of them
is divided according to the severity of the fermentation symptoms occurring into three grades marked with numbers 1, 2 i 3.
Plane type – liquid. Maintaining a liquid state after 24 hours is not a desired symptom, as it generally demonstrates the poverty of milk in lactic acid bacteria, the brake of harmful microbes. Type pl3 is like a transition to w1 (bloating). If there are many samples of this type, the cheese is prone to gas and excessive meshing.
Gelatinous type. The gelatinous curd is a sign of pure lactic acid fermentation and the most desirable fermentation in cheese making. We classify it according to this, whether the clot is completely uniform, or scratched with more or less smudges or gas bubbles by three degrees: gl1,,gl2 i gl3, of which gl1 is the most exemplary. The classification table provides a detailed explanation of the assessment method.
Typ s – caseous. Cheesecake more or less shrunken. In the milk s2 and s3, a greenish or cloudy whey with low acidity was released. Rennet-producing bacteria are also active here. The s1 type is of no concern, on the other hand, s2 and s3 are uncertain and not suitable for the production of cottage cheese.
Type z – grainy. Semolina or granular clot under the influence of kernels along with other bacteria. It is characterized by unstable milk and low in lactic acid bacteria, what happens most often with us in winter. The curd z1 is sometimes so finely gritty, that it can be overlooked and mistaken for gl1. Z2 milk, which contains coarser lumps surrounded by whey, is unreliable. Curdled milk is dangerous. The cheesecake in it is tousled into coarser flakes, whey is cloudy.
Z1 type milk in small quantities presents no danger in processing.
W-bloating type. It is a bloat milk due to the prevalence of coliforms and aerogenes. The escaping gases disrupted the clot to a greater or lesser extent, sometimes they even threw it out of the test tube; whey is often cloudy.
It is possible to use the milk w1 when it is skilfully processed, for a small amount of the bloating bacteria will be suppressed by the right lactic acid bacteria. W2 and w3 milk are dangerous, because we get bloated cheeses from it.
If you notice bloating milk in the cheese factory, should be investigated immediately, where does it come from, then carry out an inspection, to find out the cause of the defect, and exclude milk from delivery, until the defects are removed.