Milk powder was used as raw material, through the process of reconstitution, pasteurization, inoculation ,fermentation, etc, the casein of the milk was transformed into curd by lactics.
Another version, called ultra-high temperature processing, or ultra pasteurization, blasts the milk with considerably higher temperatures over just a few seconds.
This led to the invention of pasteurization, as you all know from your middle school science classes, but it also led to an understanding that fermentation was a biological process involving living organisms.
Raw milk can carry microbes that are the sources of deadly diseases, so in order to kill as many of those microbes as possible, and keep milk fresh longer, we use a technique called pasteurization.