Yes! I made that pun! As a Frenchmen abroad I wonder why it took me so long to come up with today’s theme for the Microbial Advent Calendar. For day 21 we look at the rightfully placed fascination of scientists with cheese and their associated microorganisms.
There is so much to say about cheese…
Its origin goes quite far back, it is thought that cheese was discovered around 8000 BCE when sheep were first domesticated. Then by the time the Greeks built their empire it was an everyday food and by the time the Romans took over it was considered an Art. Apparently, Pliny’s Natural History (77BCE) has a whole chapter on cheese! Local weather was the major factor in the production and more importantly storing of cheese, the earliest cheeses were likely to have been quite sour and salty, similar in texture to rustic cottage cheese or feta, a crumbly, flavorfull Greek cheese. Cheese produced in Europe, where climates are cooler than the Middle East, required less salt for preservation. With less salt and acidity, the cheese became a suitable environment for useful microbes and moulds, giving aged cheeses their respective flavours*.
Today cheese is still an art, but to in new ways with an extended understanding of the different processes behind each type of cheese. Cooked or not, matured or not, use of microorganisms or not… Yes indeed, if some cheeses like camembert or brie are unsurprisingly made, or matured, thanks to fungi (Penicillium to be more precise) much more are made with bacteria. In the first step of the cheese preparation, curdling, microbial starters are used, they belong to the Lactococcus, Lactobacillus, or Streptococcus families. Swiss starter cultures also include Propionibacter shermani, which produces carbon dioxide gas bubbles during ageing, giving Swiss cheese or Emmental its holes. During curdling, milk is separated into solid curds and liquid whey, those will then be used in a variety of different process to make this or this cheese.
Today, this nerdy microbiologists had a particular look at the effect of bacteria on the aroma and the ripening process of cheese (here and here). But it even goes further, cheese has been found to be a perfect playing ground to study microbiology interactions, and a myriad of studies looked at the mechanisms involved in those closed and easily manipulable environments. Studies looked at the interaction between phages and bacteria in a closed system (here), other on the effect and transfer of antibiotic resistance within the cheese community but also with our gut microbiota (here and here).