Pasta sauce is perhaps the quintessential “How long will it keep?” product.  If you’re cooking for a small household—1-3 diners—you’re not likely to polish off a large jar at one meal, and it’s hard to find a small jar on store shelves. Therefore, you may regularly find yourself left with half a jar. But how soon are you going to want pasta again?  You put the remainder in your fridge, and, before you know it, ten days have passed. Now what?  Is it still good?  Would it be obvious if it weren't?  Can pasta sauce turn dangerous?  Probably not, you think. On the other hand, it probably won’t taste too good anymore, so maybe it should be tossed. But, then again, it would be a pity to waste a half jar.  And round and round you go.