What exactly is the white coating on the skin of a Salami?
Mold?
Fungus?
What is it’s purpose?
phox
Depends on what the salami has been used for before you encounter it…
I was gonna ask JDT but he’s gone. 
I’ll be shocked if it isn’t a mold.
I would doubt that there is a purpose, as that would imply intent on the part of someone/thing to make something happen. What can’t it just be that mold grows on stuff which has been exposed to the air too long. Check my fridge. ipso facto
The USDA says:
“Some salamis – San Francisco, Italian and Eastern European types – have a characteristic thin, white
mold coating.”
See http://www.fsis.usda.gov/OA/FAQ/hotlinefaq1.htm.
Now as for how the mold gets there…
Jeyen
Yup it’s mold.
Properly made salami is a fermented meat product, it needs no refigeration and was orginally a way of storing meat for the winter, rather like beef jerky.
I suspect that in many supermarkets they only put it in the chiller bacause it’s either crap or people wouldn’t but it otherwize.
Personally I like my salami hung up so it gets nice and dry and chewy…Mmmmmm.