What is happening in your glass happened is a process called curdling.

But why does this happen!?

Well, it all comes down to science. Milk is made up of bunch of different things including fat, protein and sugar, and even has good bacteria in it. Curdling happens when a few of those things interact in the milk. Here’s a breakdown of what’s happening:

  • The bacteria starts getting old. Especially if the milk was left in warm place, it can increase the speed of this process. (So be sure to store your milk properly)
  • That bacteria starts to eats the sugar (lactose) in the milk and produces something called lactic acid.
  • This acid causes the protein to clump together
  • Separation occurs between the curdled milk (the lumpy proteins) and the other liquid that’s called whey.
  • This process also is the reason for the smell (production of the acids)

So no, that’s not cheese forming- it’s the protein in the milk floating on the whey, so please do not try to consume it.

However, the premise of creating cheese starts a similar way. Bacteria culture (not at all the same bacterial as you had in your glass at home) is added to milk to get that bacteria to start consuming that sugar (lactose) and producing lactic acid and an enzyme is added. Then, the solid part is removed from the whey (the liquid) and depending on what type of cheese is being made, there are different processes from there.

Who knew all of this interesting stuff could happen in a simple glass of milk!?