This is what’s special about mustard: it kind of hurts and, well… it’s supposed to. Mustard is hot, it’s an irritant and unlike black pepper and chile (the burn of which is only really felt on contact or when heated) mustard is volatile at room temperature so we need only open a jar and dangle it beneath our nasal passages to sense the burn. It’s a chemical defense common to Brassicaceae (or the Cruciferae, if you are really into old-school taxonomy), the cabbage family, and you’ll smell, taste, and feel it throughout. This family includes radishes, turnips, capers, horseradish, wasabi, and all the cabbages (kale, broccoli, cauliflower, Brussels sprouts, bok choy). The mustard oils, which give the plants their flavor, are unique to the Brassicaceae. The tingle of radishes? Mustard oils. The stink of overcooked Brussels sprouts? Mustard oils. And every time you ask me if a particular mustard has horseradish or wasabi in it? Well… kind of. It’s all composed of the same stuff.
The beauty of the mustard oils is what they are before and how they become. The cells of the cabbages (I use this term broadly for all the members of the aforementioned family) contain sulfurous compounds, glucosinolates. In their stable state the glucosinolates are unreactive, but here’s where the cabbages are quite clever: they have specialized cells that contain the enzyme myosin. The sole purpose of these cells is to hang out, metabolize, and hold onto that myosin until the plant is damaged, usually by something trying to eat it. Then, the cell walls break. The myosin then comes in contact with the glucosinolates, breaking them down into volatile mustard oils. The intent, from the cabbages’ point of view, is to deter herbivory. As we know, mustard oils burn the nose and mouth and as any rabbit fancier or Beatrix Potter fan knows, they give little herbivores tummy aches.
Not to say that we, as humans, are more clever than plants — that simply could never be — but we are a little masochistic when it comes to life’s pleasures, like food, and naturally seek flavors that hurt a little. (Don’t buy my fake psychology? Stop asking for cheese with a “bite” or salami with a “kick.”) Mustard, the condiment, is prepared by treating the seeds, ground or whole, with some sort of acid; usually vinegar or wine. The acid reduces the intensity of the mustard oils, making it palatable and tasty without removing the burn we all love. Mustard, as a plant and a preparation, is native to the Old World, and I stress that this includes Europe, where it has been used a condiment since ancient Rome, probably earlier, before Europeans had traveled to Asia and found spices or the New World and found chiles: an unpillaged flavor! Turning mustard seed into a condiment was probably introduced to France before it was France and, naturally, by the Romans (this may make it a re-pillaged flavor), but this is blog, so who needs facts? And even when you can’t buy a pretzel or an egg roll without being offered mustard, Burgundy (the capital of which is Dijon!) remains the cultural epicenter of mustard.
If, for some reason, you are still reading this, you are probably waiting for me to explain the chemical properties of mustard that make it an emulsifier or its use in Middle Eastern and Asian cuisine. Well, I am not. I will, however, try to sell you something in another blog post.