If the milk is old the curdling is a natural stage of turning sour and cannot be reversed, if its a small amout then it should be disguarded, if you have several pints then you could turn the curds (lumpy bits) into cheese, they whey (watery bit) can be fed to pigs if you have any.
curdled milk
It is rotten milk
It is rotten milk
sour
Finding the milk was curdled meant I had to have toast and not cereal for my breakfast.
curdled milk
Whey or milk plasma is the liquid remaining after milk has been curdled and strained.
lactic
curdled
can rotten coconut milk hurt your stomach?
curdled milk is one of the ingredients
Posset