we cant say "water under cheese", it will be word by word translation! I don't know how they get this water, how the procedure is, but the word "peyniraltı suyu" mean just "whey" -and ı am sure of that!
in the Production of cheese appears also water.It comes from milk and it is very helpful for health.Cheese swims in this water and not get dry.
From this water can get powder.
I think, there isn't any kind of wort in English.