So, what's going on here? Well, it all comes down to the chemistry of mustard. You see, mustard contains volatile compounds that are super sensitive to temperature and humidity. When you store it in the fridge, these compounds start to break down, and the flavor and aroma of the mustard begin to fade away.
Think of it like a good wine, you wouldn't store a fine wine in the fridge, would you? I mean, some wines are meant to be chilled, but not all of them. Mustard is kind of like that, it needs to be stored in a cool, dry place, like a pantry or a cupboard. This way, the flavors and aromas can mature and develop, like a good wine.
Now, you might be thinking, but what about food safety? Don't worry, storing mustard at room temperature won't make it go bad or anything. In fact, most mustard brands are designed to be stored at room temperature, and they'll still be perfectly safe to eat. So, no need to worry about food poisoning or anything like that.