Mustard Facts - How can you tell when it has gone bad?

So here's a question I've gotten a bunch of times before, being an apparent expert on mustard; how do you know when your mustard has gone bad? I've had a basic idea of it before - "Its bad when, ya know, it doesn't taste mustardy anymore?" I've finally went and began research into the subject, and found out the answers to the question any mustard collector would ask.

The Transportation Information Service, or the Fachinformationen der Deutschen Transportversicherer, is a German online service for sea transport in the German area. As a part of this, the TIS has information on transport of specific cargoes. Under mustard (apparently, Germany transports so much mustard it needs a specific cargo page), it had a number of points that can help you keep your mustard! Here's a quick overview of the cargo info:

• Mustard must be stored under 20º C (68º F)
• If it's stored above this temperature, it will quickly lose flavor
• There's three ways of knowing if mustard is bad:
• If the jar is cracked, of course
• If there's water on the top
• If it's dully coloured/gray
• Light, exposure to oxygen and exposure to heat can all ruin your mustard  

Take these protips and run with 'em, and your mustard will stay fresh for months to come.