We've got a small jar of Vegemite that the kids are slowly nibbling away at, and I just realized it has a best-before date of three months ago. At the current rate of consumption, there's another six months to go before it's gone. We're keeping it in the fridge, and it shows no visible signs of going bad so far.
How long is it safe to keep, and how do we know it's gone bad? Bear in mind this is pretty funky-smelling stuff in the first place.
Also, just how bad an idea is it to reuse a knife that's previously been used to spread butter to scoop out Vegemite?
Update: On further inspection, the date on the bottom of the jar is just a date, it's not labeled as "best before" or "use by" anywhere on the jar. Definitely not the date of manufacture though, and the official Vegemite FAQ implies it's a best-before date.
Also, this somewhat amusing Metafilter thread about whether somebody should eat seven-year-old Vegemite, the general consensus being "it's probably OK".
Best Answer
Best-before dates aren't the same as use-by dates. Whilst you shouldn't consume a product after it's use-by date, best-before dates are more about quality than safety. Basically, after the best-before date, the product may start to deteriorate in terms of flavour, but that doesn't mean you can't still eat it.
I'd expect that the salt content of Vegemite would keep it sound for a long time. I've certainly had half-eaten jars of Marmite (sorry, I'm a Marmite guy, not Vegemite) kicking around in the pantry for way longer than they ought, and they've been just fine.
Butter and breadcrumbs from the knife may well develop mould if they're left in the jar for a while, but that would normally just be on the surface and easily removed. Much better to remove crumbs before they get to that stage - or, easier, just use a clean knife.