Pepper Heat Vs. Horseradish Heat: PepperScale Showdown

Horseradish and chili peppers stimulate the same set of sensory receptors (called polymodal nociceptors) in the mouth and nose, which is why we register both of them as hot with both spices, the ability to cause burning is likely the plant’s self-protection mechanism to avoid being eaten by various organisms. But is there more to the story? How do we feel the heat? Can you temper the spiciness the same way? We break it all down in another PepperScale Showdown.

What causes the spicy flavor in horseradish?

When horseradish is grated or otherwise cut, its cells break open to release two compounds: an enzyme called myrosinase and a glucosinolate called sinigrin. Myrosinase breaks the sinigrin down to form allyl isothiocyanate, which is the source of heat in horseradish. Allyl isothiocyanate also provides the heat in radishes and mustard, both of which belong to the same family as horseradish

What causes the spicy flavor in chili peppers?

The heat from chili peppers comes from the compound capsaicin. Contrary to popular belief, most of a pepper’s capsaicin is contained in the white membranes that connect the seeds to the walls of the chili pepper. The walls themselves contain much less capsaicin. Chili pepper seeds contain no capsaicin at all (though they may taste hot due to being in contact with the membrane).  

How do the compounds in horseradish and in chili peppers affect the body?

Air and saliva oxidize allyl isothiocyanate, which causes it to irritate the mucous membranes and produce the heat that you detect when you consume horseradish. 

The sensory receptors that allyl isothiocyanate and capsaicin act upon are sensitive to mechanical stimulation and to temperature. When the receptors are chemically stimulated, they can interpret the stimulation as mechanical stimulation like being cut or as temperature extremes like being burned.

The body reacts to the stimuli in the same way that it would respond to a cut or a burn, which is by flushing the nasal passages and sweating to cool itself down. It’s why some believe chili peppers are perfect for flushing out a cold (though careful with that old wive’s tail).

It is worth mentioning that menthol is a third compound that acts on the same receptors, only it causes a sensation of coolness rather than one of heat. 

With both allyl isothiocyanate and capsaicin, the hot sensation results in an endorphin rush that gives the person eating horseradish or chili peppers a sense of euphoria. 

Do you temper the heat from horseradish and the heat from chili peppers in the same way?

Horseradish and chili peppers may work on the same sensory receptors but they are different compounds. If you are trying to temper the heat, you will need to take different approaches.

With horseradish, the allyl isothiocyanate is volatile. The volatility means that all you have to do is wait for it to evaporate. Over the course of about 15 minutes, freshly grated horseradish will start to lose its pungency. If you want to preserve the heat, you will need to take steps to prevent the evaporation. In other words, it will temper its own heat naturally without you having to do anything. Allyl isothiocyanate is also water-soluble, which means that the heat can be washed away with a water-based liquid. 

Capsaicin is not volatile, which means that waiting will not provide relief from the burn — it won’t evaporate. In addition, it is oil soluble rather than water soluble. Oil solubility means that you can’t wash it away with water but you can get rid of it with milk. Milk contains casein, which binds with capsaicin allowing you to wash it away. You can use alcohol for the same purpose — it dissolves the oil that allows capsaicin to repel water. 

UPDATE NOTICE: This post was updated on March 19, 2022 to include new content.
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