A Staff Report from the Straight Dope Science Advisory Board

What makes mustard so mustardy?

September 14, 2004

Dear Straight Dope:

With all of the reports coming in from Iraq about chemical weapon and the like, it reminds me that I've always wanted to know what exactly "mustard gas" is. Does it have any relation to the food product? Is it one of the 57 varieties? is there such thing as "ketchup gas?"

Dear Straight Dope:

I'd like to know about mustard. Not that adulterated sludge that is commonly slathered over hotdogs, but the dangerously keen paste that, upon consumption of just a little too much, gives the sensation that one has lava emerging from ones nose. Same goes with horseradish sauce and, to the greatest extent, wasabi. What gives these condiments such crippling power?

Dear Straight Dope:

Living in Northern California, I have exposure to many kinds of ethnic foods. While I find that I can handle a healthy dollop of wasabi on anything, even the slightest bit of jalapeno sauce makes my tongue burn for quite some time. Why is this? I know that jalapenos have capsaicin in them, does wasabi?

SDStaff Una replies:

I wondered about all of these topics as well — I originally thought mustard must contain a form of capsaicin, the fiery component of pepper, even though the heat seemed to be a different type. I was also curious about whether there was any connection between mustard and mustard gas. After all, capsaicin is used in some self-defense sprays. Finally, having experienced wasabi at a local Japanese restaurant, I wondered what made this other food so wonderfully hot. So I did some investigation on these issues for all of us. Here's what I discovered. Mustard's heat derives from mustard oils, which are released from mustard seed when the latter is crushed. These oils contain chemicals and enzymes that, when combined with water, react to liberate compounds called isothiocyanates, which give mustard its heat. That's why, when you mix dry mustard with water, the heat of the mustard paste starts out low but slowly increases, reaching a peak in about 10-15 minutes.

Depending on the type of seed and other variables, somewhere between 0.6% and 1% of mustard seed is made up of isothiocyanates. Consumed in quantity, these chemicals irritate the nasal passages as well as the throat and eyes. For just that reason mustard years ago was commonly used in home remedies as a counterirritant — you chewed it to relieve a toothache or applied it in the form of a mustard plaster or poultice to alleviate respiratory ailments.

Horseradish also liberates isothiocyanates when processed, as does wasabi (sometimes known as Japanese horseradish). Due to the expense of pure wasabi, what is called wasabi in restaurants is often a mixture of horseradish, other spices, and green food coloring. Penzey's Spice Company, notable for its many fine offerings, states:

Funnily enough, the wasabi we've all been eating in Japanese restaurants for many years isn't actually made of only ground up wasabi root. It is a combination of ingredients which combine to give the bright heat and zesty flavor we all know and love mixed with soy sauce and served with sushi.

Pure Wasabi root is extremely expensive and a small jar doesn't really make very much.

In fact, Penzey's lists its "wasabi" as being made of a "(b)lend of horseradish, mustard, tapioca starch and wasabi."

Despite the similarity in name and physiological effect, the chemical weapon called mustard gas (also known as sulfur mustard) isn't made from mustard. It derives its name from the fact that it smells like mustard or horseradish, particularly if contaminated with other chemicals, and sometimes has a yellow-brown color, which might make a person think of mustard upon seeing it. However, apart from the fact that both contain sulfur, there is no direct chemical relation between the condiment and the weapon of mass destruction (WMD), despite what some believe. For example, a special online exhibit at the Louise M. Darling Biochemical Library at UCLA reports:

The pungent and irritating allyl isothiocyanate ("mustard gas") that is released from brown mustard, horseradish and other pungent vegetables has been used in war gas products and other offensive preparations both for attack and for personal defense.

As far as I can tell, this is erroneous. The Agency for Toxic Substances and Disease Registry (ATSDR), a federal agency, says that sulfur mustard "is often called by its common name, 'mustard gas,' with its chemical name being 'bis(2-chloroethyl) sulfide.'" The ATSDR goes on to say:

Sulfur mustard is a synthetic organic compound. It was first manufactured in 1822 by the action of ethene on sulfur monochloride or dichloride … The Germans produced sulfur mustard using the Meyer process, which involved treating ethylene with hypochlorous acid followed by sodium sulfide … In the United States, sulfur mustard was formerly made using the Levenstein process in which ethylene was reacted with sulphur monochloride … The most recent process used in the United States involved the formation of bis-(2-hydroxyethyl)-thioether from ethylene oxide and hydrogen sulfide.

So there you have it — not only do you know what gives mustard its bite, you can be sure a search for WMDs in your mustard jar will be fruitless. Would that we'd known the same about Iraq.


"Toxicological Profile for Sulfur Mustard," Agency for Toxic Substances and Disease Registry (ATSDR), Public Health Service, U.S. Department of Health and Human Services, 2003.

On Food and Cooking: The Science and Lore of the Kitchen by Harold McGee, 1984.

Penzey's Spices, Early Summer 2004 Catalog.

"UCLA Medicinal Spices Exhibit," http://unitproj.library.ucla.edu/bio med/spice/index.cfm

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