Lactic acid fermentation
People had been using microbial lactic acid fermentation to produce food long before Pasteur had described it. Archeological finds show that the fermentation of milk has a long history. Its first uses may have been part of the Neolithic Revolution. Milk contains lactic acid bacteria. Given the right temperature, the fermentation process will happen spontaneously.  These first farmers likely had another problem: When people become adults most lose the ability to digest fresh milk. These farmers had an interest to make milk digestible by adults. Lactic acid bacteria contain the enzymes needed to digest  lactose. During lactic acid fermentation, the number of lactic acid bacteria increase. So even if fermentation only happens for a short time, the product will contain enough enzymes, which allows the milk to be digested by adults.  Even safer was a longer fermentation, which was practiced for cheesemaking. This process was also discovered a very long time ago, which is proven by recipes for cheese production on Cuneiform scripts, the first written documents that exist, and a bit later in Babylonian and Egyptian texts.