Tonight I went out to a dinner for a friend’s birthday and almost lost my tongue.
Well, the tongue is actually ok in a physical sense, but the sensation was definitely one of loss and bewilderment. We went to a Chongqing hot pot restaurant, where a large steaming pot of broth is set in the middle of the table, and a range of raw ingredients is brought out for everyone to dip in the soup until they’re cooked. Then you eat them with a dipping sauce. The broth is far from ordinary, though — amongst chillies, goji berries, slices of ginger, leeks, garlic cloves and other, less recognisable seasonings, you also get large handfuls of Szechuan pepper.
Unlike regular, black pepper, Szechuan is not actually a peppercorn, although it does resemble one. Instead, it is the dried seedpod from the fruit of the Chinese prickly ash (Zanthoxylum simulans) shrub. Ground into a powder, this spice is one of the ingredients in Chinese five-spice seasoning.
If you’ve had dishes with this extraordinary Asian spice before, you already know what I’m talking about when I say I almost lost my tongue. After chewing on some Szechuan pepper, your mouth quickly goes tingly and numb, along with an intense flavour that is difficult to describe. After chewing on a few too many Szechuan peppers, like I did tonight by accident, you can even get a sort of drugged buzz followed by a bout of dizziness; the sensation is really quite overwhelming.
The chemical responsible for this is a naturally occurring molecule hydroxy alpha sanshool, and the feeling it creates in your mouth is called paresthesia — like the uncomfortable tingling you get when a limb “falls asleep.” Surprisingly, the molecule works by activating the touch receptors in the mouth.
Like the capsaicin in chilly peppers, which activates heat receptors and produces a burning feeling without actually applying heat, the sanshool molecule produces a feeling of vibration in the touch receptors of the lips and tongue — without actually vibrating.
In a study published in 2013, neuroscientists from University College London applied ground Szechuan peppers to the lips of some (rather willing) volunteers, and as they experienced the tingling sensation, the volunteers could compare it to the vibration of a small metal rod touching their finger and judge which frequency felt the closest to the mouth tingle.
The determined frequencies of 50 herz turned out to correspond to the frequencies that only a class of particularly sensitive touch receptors called Meissner’s corpuscles can detect. These are the types of nerve endings we commonly have concentrated on lips and fingertips.
Why the dizziness, though? I’m guessing that was probably just a sensation overload. Perhaps my tongue thought the room was spinning.