Of all the American-Chinese sauces I've made to jazz up a meal, hot mustard was by far the easiest - and most fascinating. Four simple ingredients, and you're done.
You know how tasteless those little mustard packets are - the kind you get with your Chinese dinner? Most taste like cardboard. Seriously. They have no heat or flavor to speak of, unless you like cardboard, that is.
This recipe for mustard sauce carries some heat, but it's not overpowering.
So how does this happen? I'm no food scientist, but in fairly simple terms: Mustard has an enzyme called myrosinase, which smashes organic compounds called glucosinolates into chemical compounds called isothiocyanates when combined with cold liquid, in this case, white vinegar. Together, the reaction produces the characteristic heat of hot mustard. The amount of heat produced is dependent on the type of mustard seeds, some being hotter than others.