Wasabi vs. Horseradish: Different Plants, the Same Heat Compound

In North America, that green dab next to your sushi is probably horseradish. Chowhound cites an estimate that about 99% of the wasabi sold in North America isn’t real wasabi,¹ and the swap works because the two get most of their heat from the same compound, allyl isothiocyanate.² They’re still different plants, both in the mustard family: wasabi is the rhizome of Eutrema japonicum, and horseradish is the root of Armoracia rusticana. The price gap is wide, up to $100 a pound against $3 to $5, and the sources can’t agree on which one is hotter.

Side by side

The harvest times come from different sources describing different growers, so they don’t have to agree. For each plant on its own, see wasabi and horseradish.

Same heat, different mix

Neither plant lets its heat out until its cells break. Isothiocyanates are released when the tissue is cut or grated,³ so both get grated right before use. Allyl isothiocyanate dominates in both.²

The mix isn’t identical, though. In a Lincoln University doctoral study of seven isothiocyanates, 2-phenylethyl isothiocyanate turned up only in European horseradish.² That’s a measured chemical difference. None of the sources we found tested how it changes the taste, so when you read that horseradish is “earthier” or “more bitter,” that’s someone’s description, not a finding.

Which is hotter? The sources disagree

We found no source that measured heat across fresh wasabi, tube paste and prepared horseradish. You’ll often read that horseradish’s heat lingers longer than wasabi’s. Tasting Table’s account of horseradish fading within seconds to minutes doesn’t back that up,⁸ and nothing measures the two side by side. Heat in both also depends on how long ago it was grated and, for horseradish, when the vinegar went in. Tasting Table, citing Taste of Home, says waiting several minutes before adding vinegar makes it hotter.⁸

What “wasabi” usually is

Western restaurant wasabi paste is commonly made from horseradish. Chowhound reports that the vast majority of commercial wasabi is European horseradish, mixed with mustard and citric acid and colored green to look like the real thing.¹ The labels show it. One S&B wasabi powder lists horseradish, mustard and corn starch but no wasabi.⁹ One S&B tube lists 31% horseradish and 4.5% wasabi, plus sweetener, vinegar, salt and starches.¹⁰ The Embassy of Japan’s magazine says some restaurants in Japan use a cheaper horseradish-mustard mix too.⁴

So tube “wasabi” isn’t just prepared horseradish with a green tint. It carries mustard and, in the S&B tube, sweetener and salt that a jar of prepared horseradish may not. For the details, see wasabi powder vs. paste and fresh wasabi vs. wasabi paste.

Can one stand in for the other?

Yes, and horseradish stands in for wasabi all the time. It’s the usual substitute for true wasabi.

Tasting Table’s ratio uses less wasabi paste than horseradish, which fits its view that wasabi is the more intense of the two,⁷ but it’s specific to cocktail sauce. See wasabi substitutes and horseradish substitutes.

Color. Commercial wasabi is dyed green to look like the real thing. Grated horseradish is creamy white, so when looks matter, they’re easy to tell apart.

Storage

• Fresh wasabi rhizome. Grate only what you need, just before serving. We didn’t find a sourced fridge life for a whole rhizome. The Lincoln University study found that rhizomes frozen at −10°C or colder for two months kept their original levels of heat compounds.²
• Grated horseradish. ATK found that the vinegar in prepared horseradish keeps its heat by slowing the enzyme down, and that a homemade batch holds its heat for up to two weeks in the fridge.⁶
• Whole horseradish root. We found no sourced storage time.

You’ll sometimes see both roots given “a few months” in the fridge and grated wasabi “a couple of days.” We couldn’t find a source for the first, and the second conflicts with the 15-minute figure above.¹

When to use which

Wasabi goes mainly with sushi and sashimi. The Embassy of Japan’s magazine says it gets rid of fishy smells and brings out the fresh flavor of seafood.⁴ Fresh wasabi is worth the price where you’ll actually notice its sweetness and quick-fading heat, like with good raw fish. You’ll also see claims that wasabi protects against food poisoning. None of the sources we reviewed support that as a food-safety measure, so we won’t repeat it as one.

Horseradish goes where a bold, sinus-clearing heat suits the food: with roast beef, in cocktail sauce, in Bloody Marys and in creamy sauces. At the Passover seder, horseradish is widely used as maror, the bitter herb. Rabbi Ari Zivotofsky writes in Jewish Action that the custom spread among Eastern European Jews because lettuce wasn’t available before Passover.¹² For more, see cooking with horseradish and cooking with wasabi.

What isn’t known

• We found no measured heat comparison of fresh wasabi, horseradish-based wasabi and prepared horseradish.
• No source we found has tested how 2-phenylethyl isothiocyanate changes horseradish’s flavor.
• No sourced fridge life for a whole wasabi rhizome or horseradish root.

Related

• Wasabi, horseradish and horseradish powder
• Wasabi powder vs. paste and fresh wasabi vs. wasabi paste
• Wasabi substitutes and horseradish substitutes
• Too much wasabi? How to rescue a dish.
• Mustard powder, which gets its heat from the same compound, and Japanese spices