You've taken your first bite of boiled fish with green pepper sauce at Chengdu Taste in the San Gabriel Valley and you notice something odd. Your lips. They're burning.
But there's more than that. They feel different. You know it's the Szechuan peppercorns, the taste of which is often described as tingling. But wait, "tingling" and "burning" are not flavors, are they? What's going on here?
That may seem like a simple enough question, but it took until just recently for scientists to decode what was going on. University College London researchers have published a paper on the topic in the Proceedings of the Royal Society B, which was reported on the blog of the Smithsonian magazine. The paper, incidentally, is titled "Food Vibrations," which proves that science need not be dry.
It's fascinating reading, if you've got a wonky turn of mind. It turns out that Szechuan peppercorns contain a chemical compound known as hydroxy-alpha-sanshool, which stimulates tactile -- not flavor -- receptors in the mouth and lips.
To study the effect of the peppercorns, the scientists lined up 28 volunteers who had their lips painted with an extract of Szechuan peppercorns. In an ingenious twist, they then had the volunteers hold a miniature vibrating tool to their lips to try to mimic the frequency of the tingle from the peppercorns. By identifying that frequency (roughly 50 beats per minute), they could determine exactly which group of receptors were affected.
This is very similar to the reaction provoked by capsaicin -- the active ingredient in chiles, which make your mouth feel like it's burning even though there's no flame. Except that capsaicin affects a different set of receptors -- the same ones that sense pain from burning.
So, in essence, what Szechuan cooks have done is trick your body into convincing your mind that A) it's on fire and B) it's vibrating madly, even though there's no flame and no motion.