Why do Sainsburys put a sell-by date on sour cream?

Or water that's been filtered through volcanic rocks for 2000 years!

Try leaving some for a few weeks and I'm sure you'll find out! Doesn't take long before it goes mouldy.

Or cheese and meat thats matured for 6 months in some filthy shed in France - quick it's only got 2 days left before it becomes deadly, sell sell sell!!

Same thing with rock salt, been under the ground for hundreds of thousands of years, but sell by date in 2009! Seems like they just found it intime before is goes off!!

Chris