As previously noted, we perceive the spontaneous souring of milk, that at times it becomes acidic from top to bottom, which testifies, that aerobes are active here. In addition to lactic acid, they also produce acetic acid in varying amounts, bursztynowy, form and slightly disturb the protein. They hardly ever develop at temperatures below 15 ° C, while live with 25 do 40°C. Some of them produce significant amounts of gas from milk sugar, so that the milk clot is agitated, the cottage cheese is so saturated with gases, that it rises to the top. The taste of milk is usually unpleasant, unclarified whey. Some of these, when they have food, that release oxygen more easily than milk sugar, they break them down without disturbing the milk sugar. We use this in cheese making. Because when we expect, that milk contains a lot of bloating bacteria, we put saltpeter to it (10 do 40 g na 100 l let him), to keep the cheeses from gas. Gases are not formed from the decomposed saltpeter, the sugar, meanwhile, will be broken down by non-bloating bacteria.
Some strains of bacteria enumerated here withstand heating above 70 ° C and therefore thrive in non-chilled pasteurized milk. There are a variety of aerobes belonging to the genera: Microbacoccus (Tetracoccus) i Micro-bacterium. They are more or less harmful in cheese making. They accompany the sloppy and storage of milk at a temperature above 15 °C.
In this group, we find a variety of udder kernels: harmful and harmless. Some cause mastitis. Too harmless, and even the kernel Micrococcus acido-proteolyticus is considered useful in cheese making, that is, acid-rennet. He sours the milk and cuts it with rennet leaven. Its enzyme works even at temperatures close to 0 ° C.
Another kernel necessary for the maturation of Camembert cheeses and giving them their specific aroma and color processes milk sugar and breaks down the protein. It creates the so-called. red = rouge. We will get to know it better by discussing the production of Camembert cheeses.
Various strains of Bact fecal bacteria are also included here. coli commune i Bact. lactis aerogenes. Both species live in the digestive tract and get into milk with faeces, especially when the cattle suffer from diarrhea and splash themselves and their surroundings with faeces. Faecal bacteria still grows at 15 ° C, although, by nature, their optimum is at 38 ° C (body temperature).
Bact. coli are shaped like short, mobile sticks. Completely similar to them, but the aerogenes are immobile. Both species produce little lactic acid, but a lot of gases: coli more hydrogen than carbonic acid anhydride, aerogenes vice versa. They thrive best when exposed to air, but they can also do without it, when they find oxygen in lactose sugar, which they break down to the end. Then they give off a lot of gases, they gasp, they even rip the cheeses apart. They are among the largest pests in cheese making, and consumed in sour milk can cause gastrointestinal disorders in humans.
Changes in the taste of milk made by them manifest themselves differently depending on the number and coexistence with other microorganisms.. First, they give the milk a sweet and sour taste, which is even pleasant and refreshing at times, the aroma sometimes resembles wild strawberries. However, sometimes the milk tastes unpleasant right from the start, smacks of the stable, swedish, beets, cabbage. Pasteurization above 65 ° C destroys these pests.
Coliforms and aerogenes cannot tolerate as much acid as pure lactic acid bacteria. This is used in cheese making, e.g. the rennet mortar is acidified from the beginning with the varieties of strongly acidifying bacteria, she floods it with casol or vinegar.
Prevention of milk infection with bloating faecal bacteria is primarily based on such nutrition, so that the feces are of normal hardness. Therefore, cattle should be fed with healthy feed and diarrhea should be avoided by all means. Bact. aerogenes can be found almost in pure culture in the remains of moist concentrated feed, e.g. bran left in uncleaned grooves, where they ferment. Seedbeds of these bacteria, making our cheese-making in many places hopeless, there are countless dunghills not included in concrete tanks, contaminating the environment, even water in the wells. No wonder either, that in summer there is generally more puffing milk than normally sour milk.