You will know when it's bad when it gets "slimy" to the touch on the outside. Is it in a block or crumbled? The crumbled occasionally lasts a bit longer because they dry it out some before they crumble it for plastic packaging. If it's in a wedge/block, keep it firmly wrapped in plastic -- and EVERYTIME you unwrap it, put a fresh clean piece of saran (or your plastic of choice) on it. Don't reuse. Also, don't store in Foil... But, again, you'll know it's bad when it gets slimy, sometimes it will even get a reddish/yellow/or orange film on it -- which is a different kind of mold from the mold that grew in the cheese. (I love both Gorg. and Bleu and Roquefort...
