Why does chili make you sweat, but wasabi doesn't? Decoding the mystery of spices through plant survival strategies @Chiko-chan (Former professor, 716th day of retirement)
The "spices" that soba lovers insist on
As I have mentioned before, I am quite the "soba enthusiast" and love both cold and hot soba. However, the spices served with them differ slightly. For hot soba, excluding Hanamaki soba, shichimi togarashi (seven-flavor chili pepper) is the standard, while for cold soba, it is undoubtedly wasabi (Note 1). Once, a gourmet friend taught me, "If it's good wasabi, it's delicious to put a little bit on the soba instead of dissolving it in the dipping sauce." When I actually tried it, I could feel the flavor of the wasabi and the taste of the soba itself much more clearly (Note 2). I was also once advised, "Before you start eating, try tasting just one strand of soba without anything on it." This was also a quite interesting experience that allowed me to clearly understand the aroma and sweetness of the soba itself.
<Note 1> Hanamaki soba is a hot soba dish, but it is characterized by being sprinkled with plenty of nori seaweed and served with wasabi. I always ask for extra of both and enjoy them while dissolving them into the dashi broth. By the way, the New Year's Eve soba from Kawadoya that you can get during the Setsubun festival at Yoshida Shrine in Kyoto was also served in the Hanamaki style with nori and wasabi. However, I was disappointed to hear that it was canceled during the COVID-19 pandemic. Hoping it would return along with the Eho-maki from Yamahide, I looked it up and was happy to find that it had returned this year for the first time in five years.
<Note 2> This is about sashimi, not soba, but the legendary gourmet Kitaoji Rosanjin recommended that when eating sashimi, instead of dissolving wasabi in soy sauce, you should place an appropriate amount directly on the sashimi, then add a little soy sauce on top before putting it in your mouth. This creates a time-delayed sensory experience where you first smell the aroma of the wasabi, followed by the saltiness of the soy sauce and the umami of the fish.
Learning why chili makes you sweat on "Chiko-chan ni Shikarareru"
This time, the topic is about chili and wasabi. The other day, I watched an episode of the NHK program "Chiko-chan ni Shikarareru" on the theme, "Why do you sweat when you eat chili, but not when you eat wasabi?" Even though I eat both regularly, I had never properly thought about the reason. The program explained in an easy-to-understand way what the difference is between the two, why we sweat in the first place, and why that difference emerged. Personally, I also wanted to know why pepper makes you sneeze or why Japanese pepper (sansho) makes your tongue numb, but it seems there wasn't enough time for that (laughs). (Please also see the title photo and the photo below: Note 1)
The true nature of the "spiciness" that spices trigger
First, regarding "spiciness" itself, human taste is classified into five categories: sweet, salty, sour, bitter, and umami. However, "spiciness," while generally spoken of as a taste, is actually a sensation that belongs to "pain," not taste. The essence of spiciness is the sensation of "pain" or "heat" caused by stimulating the trigeminal nerve present in the mucous membranes of the mouth and nose. And the receptors that receive that stimulation are different for chili and wasabi. In other words, these two plants use completely different chemical components and different receptors to make humans feel "spicy." (Please also see the photo below)
What was particularly impressive on the program was the explanation of the chili's spicy component, capsaicin, and its receptor, "TRPV1." This receptor detects not only "pain" but also "heat above 43°C." When capsaicin stimulates TRPV1, the brain is tricked into feeling "heat" at the same time as "pain," even though it is not actually hot. As a result, the body activates the sympathetic nervous system to try to lower body temperature, causing sweating. On the other hand, the spicy component of wasabi is allyl isothiocyanate, which stimulates a different receptor called "TRPA1." TRPA1 mainly reacts to "pain" and has almost no sensitivity to heat itself. Therefore, when you eat wasabi, the brain feels "pain" or a "sharp sting," but it does not perceive it as "hot." In other words, the illusion that body temperature has risen does not occur, which is why it does not lead to a sweating reaction like chili. (Please also see the photo below)
<Note 3> Capsaicin is a lipophilic molecule that dissolves easily in oil, and once it adheres to the mucous membrane of the tongue, it is difficult to wash away with water. Therefore, the spiciness lingers in the mouth for a long time, bringing a persistent sensation of heat. On the other hand, allyl isothiocyanate is highly volatile, and it creates that sharp stimulation by vaporizing in the mouth and passing through the nose. Wasabi's spiciness is, so to speak, a "spiciness that goes through the nose," and it subsides relatively quickly if it is exposed to air and disperses. This difference in properties is why chili's spiciness feels like it stays for a long time, while wasabi's spiciness feels like it passes through in an instant.
Are spices chemical weapons of plants? — The evolutionary strategies of chili and wasabi
What was even more interesting was the evolutionary story of why these differences emerged between chili and wasabi. In other words, plants have acquired different "spiciness" within their respective survival strategies. In a sense, these can be called "chemical weapons" developed to avoid being eaten by animals. To protect themselves from herbivores and insects, plants have acquired various secondary metabolites that act on the nervous systems of animals during the process of evolution. What is interesting is that humans are conversely enjoying those "rejection signals" as an accent of "deliciousness" (laughs).
First, regarding chili, its goal was to keep away mammals that would crush its seeds, while having birds, which swallow the seeds whole and carry them far away, eat them. Because birds' receptors have low sensitivity, birds do not feel the spiciness when they eat chili. Moreover, because birds swallow the seeds without chewing, the seeds are carried intact. In other words, for chili, being eaten by birds was advantageous for spreading its distribution. On the other hand, mammals are not desirable for chili because they crush the seeds. Therefore, individuals with a lot of capsaicin, which feels spicy to mammals but not to birds, survived through evolution. In contrast, wasabi must protect its important organ, the rhizome that grows underground. It has growth points there and increases by division, so being eaten is a major blow to the plant. In other words, wasabi was a plant that wanted to be "not eaten" as widely as possible, rather than choosing and allowing birds or mammals. Therefore, it is said that it developed allyl isothiocyanate, which many animals dislike, and evolved in a direction to protect its roots. (Please also see the photo below)
For a while now, I have started using not only chili peppers and wasabi as spicy seasonings, but also yuzu kosho and horseradish. I often add yuzu kosho to hot pot and horseradish to roast beef, but I only learned about both of them after becoming an adult. Yuzu kosho is in the chili pepper family, and horseradish is a type of wasabi (I used to call it 'mountain wasabi' in Hokkaido), so yuzu kosho has a sudorific effect as mentioned above. While writing this, I suddenly got an irresistible craving for 'chicken mizutaki' eaten with yuzu kosho. Well then, until next time.
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Note 1: From the NHK 'Chiko-chan ni Shikarareru!' special feature 'The Mystery of Chili Peppers'