The bad cheese is orange, the good cheese is yellow or white. More seriously, the orange cheese melts at lower temperatures and doesn’t separate after melting. It can be good for grilled sandwiches and I’m told you can add small amounts to cheese sauces to prevent them from separating when stored in the fridge without impacting the flavor.
https://en.wikipedia.org/wiki/Arab_conquest_of_Egypt
It was pretty quick, just 639 to 642. The western half of the Roman Empire had already collapsed and the eastern half wasn’t doing much better.