I just cleaned the fridge for the second time in six weeks. Now, I understand some of the dirt, like in the egg compartments, because eggs sweat a bit, so to speak. But how did I end up with all this yellow crud on the bottom shelf? Everything in the fridge is contained in a jar or a tupperware container or suchlike; nothing’s spilling. 
[Anne Elk] My theedy[/Anne Elk] is that there is a certain amount of condensation all over that runs down to the bottom of the fridge. There are going be some bacteria in there, no matter how much you clean, and they combine with the water to produce little petri dishes of refrigerator crud.
Yum.
I see. Thank you. (Sorry 'bout the late response.)