Horseradish is one of those flavors that evokes a strongly polar emotional response in people. There is nothing mild or subtle about it: it's abrasive, and you either love that or you don't.
The science...Horseradish (amoracia rusticana) is a root vegetable in the cabbage family. It's native to western Asia and southeast Europe, though it now grows quite aggressively in many parts of the world. It was prized in Greek mythology for its medicinal and culinary purposes. It's been used as a pain reliever, a cough remedy, and (surprisingly) an aphrodisiac. In the Passover Seder it is used to symbolize the bitterness of Jewish slavery in Egypt. Intact, horseradish barely has an aroma. But when the plant cells are damaged during grating or processing, the enzyme myrosinase is released which catalyzes the degradation of a compound in the horseradish known as sinigrin into allyl isothiocyanate, also known as mustard oil. Therefore the pungency of your preparation will depend directly on how finely you grate it and how many cells you damage in the process. Think of it as a fantastic little mustard oil producing factory, ready to pump out a bunch of mustard oil on command. Or think of it like the chemical reaction that happens when you crack a glow stick, allowing the two stockpiles of chemicals inside to intermingle and create a glowing product. Evolutionarily, this adaptation of a noxious product created upon cellular damage probably served to deter potential predators from eating the plant. It is a defense found in many brassicas, including cabbages, kales, and infamously, wasabi and mustards. It is especially active in young, actively growing tissue. The acidity of vinegar halts the enzymatic activity of myrosinase and preserves whatever flavor compounds have been produced up until that point. So, if you wait a few minutes before adding vinegar to your grated horseradish, you will allow the pungency to develop stronger. If you prefer a milder preparation, add the vinegar sooner after processing. Mustard oil is also responsible for the pungency of mustard and wasabi. It is quite volatile (easily vaporizes) at room temperature, which explains why these flavors hit us so strongly in the nose (unlike, say, the heat of a chili pepper which must be heated to above 140˚F or so to become volatile and get you coughing and sneezing). Incidentally, given this tendency to vaporize, if you ever get an overly strong bite of horseradish or wasabi and experience that sinus-ripping pain, you should breathe out through your mouth (so as to prevent sending the vapor into your nose) and in through your noise (so as to prevent excessive inhalation of the compound). If you're interested in food science, be sure check out Howard McGee's definitive book On Food and Cooking: The Science and Lore of the Kitchen. Now, back to the practical!
Although it will keep just fine in the refrigerator for a few weeks, I prefer to make up just enough horseradish to use in whatever dish I'm about to prepare on that day. It doesn't take long, so unless you are using it quite frequently, I see no reason to prepare much more than you will use immediately. Prepared horseradish will lose it's flavor with time. The following makes about 2 tablespoons, adjust as necessary
Peel the skin off of the horseradish root using a vegetable peeler or a paring knife. Trim any browned bits and chop the root into small pieces. Put into a food processor and process until well ground. Use a small amount of water to facilitate the chopping if necessary (but sometimes the water just makes it stick to the sides). Remember: the finer you process the horseradish, the more pungent it will be. If you don't have a food processor, use a grater to finely process the root. Be careful! This stuff is much more potent than onions and will burn your eyes and your nose if you get too close. Add a small amount of vinegar (maybe about ½ to 1 teaspoon) and a small pinch of salt to stabilize. Again, if you wait a few minutes to add the vinegar, it will develop more pungency. Store covered in the refrigerator until use.
- 1 large coin of horseradish, about ½-inch thick (about ¾-1 oz.)
- about 1 tsp white vinegar
- pinch of salt