Most of the time he's there when they're closed...
And I would assume they clean up after the segment.
In fact, does it really matter what happens in a kitchen as long as there was a complete cleaning afterward. Otherwise, wouldn't that mean that if anyone ever cut themselves in a kitchen and bled on something (even a countertop) it would have to be thrown out?
---------------------------------------------------------------------------------------------------- Last night, I was lying back looking at the stars and I thought...where the *beep* is my ceiling???