Brownish surface layer on Greek yogurt

Might be Maillards reaction from overheated skim milk during dissolution at higher temperatures that led to bubbles when busted and the particles comes in contact with hot metal surface during pasteurization. process.

Thank you so much for the Educative insight on the above subject.
In this case: It is Full Fat Greek yogurt. The brownish discoloration normally occurs mostly outside the Plant. Holding samples in the Laboratory under control temperature are still wholesome.

Best Regards