Out of all of the American-Chinese sauces I've made recently, hot mustard was by far the easiest, yet most fascinating. Just two simple ingredients create a sauce full of flavor with mouth-scorching heat.
So how does this happen? I won't pretend I can pronounce these words or understand the whole science behind it but here's the gist: mustard has an enzyme called myrosinase which breaks down glucosinolates into isothiocyanates when combined with cold water, producing the characteristic heat of hot mustard. The amount of heat produced in this reaction is dependent on the type of mustard seeds, some being hotter than others.
For this recipe, I tried out two different hot mustard powders—Roland Chinese Hot Mustard Powder and Colman's English Mustard—then tasted them every five to ten minutes to see how the flavor and heat evolved over time.
Both seemed to reach a peak around 15 minutes after being combined with water. The Roland was the hotter of the two, packing a major heat that had the power clear even most clogged of sinuses, but the Colman's carried that hefty punch with more flavor to speak of, which, for lack of a better word, was just more mustard-y.
After their peak, they both slowly began to fade, with the mustard flavor lingering longer and longer before the heat kicked in, and that heat gradually became less pronounced but they were still both plenty hot a couple hours later.
That intense heat can be preserved to some point either by refrigerating the mustard at its peak, or adding a little vinegar to stabilize it, but this mustard is so quick and easy to put together; just equal parts mustard powder and cold water. I'd recommended making as much as you need when you need it and forget about trying to store it.
Once you try this at home, you'll have a hard time going back to those little Chinese take-out packets.