I booked a Business Class flight from Berlin to Bangkok via Istanbul. The outgoing flights turned out to be in "J" class and the return flights in "K" class.

Now I'm familiar with J from a previous booking (and it's more or less a synomym here for "Business Class") but what's the significance of K? Is it higher or lower on the food chain than J? I'm collecting miles on Lufthansa Miles & More. Will the K flights take a mileage credit hit?

If K is a negative, what steps can I take in the future to avoid getting into K? All I booked was "Business Class" on TK's website. It didn't seem like I had a say in the matter of J or K.