Microbiota found in raw milk : their origin and importance for cheese production

Sammanfattning: The microflora in milk has various different functions that affect the quality of the cheese. The tradition of making cheese is very old and for most of that time cheese has been made without adding bacteria. The aim of this essay is to summarize how the natural bacteria in the raw milk affect the quality of the cheese and to compare the differences between raw milk cheeses and pasteurized milk cheeses. This was achieved by studying literature on the subject and concluding the gathered data. The results show that various bacteria that can grow in milk may affect the cheeses in numerous ways. The ones mentioned are: lactobacillus, lactococcus, streptococci, leuconostoc, enterococci, propionibacteria, clostridia and psychrotrophic bacteria. These bacteria originate from various sources; for example, from the surrounding environment, the feed of the animals and from the animal itself. These bacteria may affect the cheese in numerous ways. Firstly, they can affect the cheese positively: e.g. by improving taste, texture or aroma. Secondly, they can also affect cheese negatively: e.g. giving rise to unwanted taste and defects like gas blowing. Due to these bacteria being killed during pasteurization there is a difference between raw milk cheese and pasteurized milk cheese, mainly in taste. For example, raw milk cheeses generally have a more distinct flavor but they also come with the risk of having harmful or even deadly pathogens in them. On the contrary, pasteurized milk often has a milder taste. Furthermore, there is also a higher degree of uniformity between batches due to the fact that the microflora in them is consistent, and therefore gives similar results each time. To conclude, it is difficult to determine which type of cheese that is optimal. It all depends on the purpose of the cheese and the preference of the consumer - something that can be heavily influenced by culture.