Horseradish is a pungent root that is a popular condiment on its own or you can use it to make the horseradish sauce that is often served with British roast beef. If you happen to run out of it and need some more before your next trip to the grocery store, there are quite a few other ingredients that you can use in its place.
Your best bet: Wasabi
Horseradish is often used as a substitute for wasabi, which is also known as Japanese horseradish. The two condiments come from related plants. The wasabi that you find in most grocery stores consists mostly of horseradish with some green food coloring added, so it makes a great stand-in if the color is not an issue. The big downside other than the fact that it is green is the fact that wasabi is somewhat milder than horseradish, which means that you will probably have to use a little more than your recipe requires for horseradish. It may also be a little more expensive than horseradish.
Use 1.5 the amount of wasabi that your recipe requires for horseradish when using it as a horseradish substitute.
A decent second choice: Spicy brown mustard
Mustard also belongs to the same family as horseradish and wasabi and gets its heat from the same compound. It is also a relative of the cabbage and the radish and these have some of the same flavor as well, though to differing degrees. Mustard’s flavor comes from the seeds of the plant, not from the root like horseradish or the rhizome like wasabi. While not all mustards are equally hot, the brown variety is one of the spicier examples and thus is the best substitute for horseradish. The color is a yellowish brown that is not too far off from the color of prepared horseradish, which makes it an effective substitute both visually and in terms of its flavor.
Use spicy brown mustard as a 1:1 substitute for horseradish.
In a pinch: Black radishes
The black radish is a variety of radish with a dull black exterior that looks as if it is covered with soot. These radishes are larger than the traditional red radishes. It is a relative to all of the substitutes above and has a very similar flavor to that of horseradish. Simply grate it and use in the same way that you would use prepared horseradish in a recipe. Note that in order to get a higher level of pungency, you will want to leave the skin intact. Removing the skin of the black radish lowers the heat level considerably.
Use black radish as a 1:1 substitute for horseradish.
Ginger is a rhizome like wasabi, though it is often referred to as a root in much the same way that wasabi is sometimes called a root. While ginger does not belong to the same family as the other horseradish substitutes listed above, it does have some heat and can pair well with many of the ingredients used in dishes that require horseradish. It should be noted that it is a bit sweeter than horseradish, so it may not be a good fit for every dish.