Hydroxy-α-sanshool
Also written sanshool, sanshools, hydroxy-alpha-sanshool, hydroxy alpha sanshool
Quick answer
The compound behind the buzzing, numbing tingle of Sichuan pepper and sanshō — not a heat at all, but a vibration, and the clearest demonstration that pungency is several unrelated phenomena.
What it does
The sensation is unlike anything else in the spice cupboard: a fizzing, buzzing tingle on the lips and tongue, often described as a mild electric current or as the feeling of a struck tuning fork held against the mouth. It builds over about thirty seconds, plateaus, and leaves a lingering numbness that dulls other sensations — including, notably, chilli heat, which is precisely why the Sichuan combination of the two works as it does rather than simply adding one burn to another. It is accompanied by a distinct citrus-peel aroma that comes from the terpene fraction rather than from the sanshools.
How it works
The physiological account, where one is established.
The sanshools act on touch-sensitive and vibration-sensitive nerve fibres rather than on the heat-and-irritation endings that capsaicin and mustard oil stimulate. That is why the sensation registers as movement rather than as temperature or pain, and why it produces numbness rather than a burn. The receptor biology is more specialised than the sources in this library adequately cover, so SpiceHQ states the nerve population and the sensation and stops there.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- low
- Fat solubility
- high
- Water solubility
- low
- Heat stability
- low
The sanshools are unstable and degrade on storage and on sustained heating, which is why Sichuan pepper is the spice most often disappointing out of a jar: an old sample smells adequately of citrus and produces no tingle at all, and the two properties fade independently. They are fat-soluble, so the traditional treatment — warming the husks briefly in oil and using the oil — extracts them efficiently, and the traditional caution against long cooking is well founded. The practical consequence is that Sichuan pepper is added late or infused into a finishing oil, that a tingle-forward dish needs recently bought stock, and that the husks rather than the black seeds carry the effect, so the gritty, bitter seeds are worth sieving out.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- SanshoPrincipal component
A different species in the same genus, used mostly as the ground ripe husk and as the young leaf. The tingle is gentler and the citrus note more prominent than in the Sichuan species.
- Sichuan pepperPrincipal component
- TimurPrincipal component
Zanthoxylum armatum, the Himalayan timur and green Sichuan pepper. The same numbing principle, often felt as more aggressive than in the red species.
What cooking and processing were measured to do to it
Findings from studies in which this compound was followed through heat, fat, water, drying or storage. Each belongs to its study and its conditions.
Frying and blooming in fat · Converts Hydroxy-α-sanshool, Hydroxy-β-sanshool, Hydroxy-ε-sanshool, Dihydroxy oxidation products, pungency
Hydroxy-α-sanshool, the principal tingling compound of Sichuan pepper, degraded markedly on heating in oil, and the more so the higher the temperature. Heat converted it into its isomers hydroxy-β-sanshool and hydroxy-ε-sanshool, and oxidised it to dihydroxy compounds.
Conditions: in oil or fat · Supercritical carbon dioxide extract of Zanthoxylum diluted in soybean oil
The tingle of Sichuan pepper is the part of it that hot oil damages, which is in keeping with the practice of infusing it gently or adding it late.
What this does not show: Read in the abstract only, which gives no temperatures, times or rates. A commercial extract in oil. Whether the isomers formed still tingle is not addressed there.
Measured on the spice
Drying · Retains Hydroxy-α-sanshool, polyphenols, flavonoids, volatile oil
Sichuan pepper given a radio-frequency heating step before hot-air drying at 50 °C showed no loss of hydroxy-α-sanshool attributable to the radio-frequency step, and kept an aroma profile similar to the fresh spice. The combined treatment also reduced the loss of polyphenols and flavonoids at the higher drying temperatures.
Conditions: Hot air at 50, 55 and 60 °C · With or without radio-frequency heating beforehand
What this does not show: Read in the abstract only. It reports the absence of a negative effect at one condition, not sanshool contents, and does not report microbial reduction.
Measured on the spice
Packaging · Depends on conditions Hydroxy-α-sanshool, total polyphenols, total flavonoids, volatile oil, antioxidant capacity
Screening single storage factors for dried Sichuan pepper, the authors found that 5 °C and an oxygen-free atmosphere significantly slowed the loss of polyphenols, flavonoids and flavour compounds, and that yellow LED light, of the four colours tried, best preserved hydroxy-α-sanshool. Combining nitrogen, yellow light and cold storage over 60 days reduced the losses of polyphenols and flavonoids by 46.88 and 57.00 per cent compared with the control and held hydroxy-α-sanshool at 19.04 mg/g.
Conditions: 5, 10, 20 and 40 °C screened; cold storage in the combined treatment · 60 days · Oxygen at 0 to 40 per cent; white, red, blue and yellow LED light; nitrogen, yellow LED and cold combined
What this does not show: Read in the abstract and conclusions only. The sanshool content of the control at 60 days is not given there, and the abstract’s percentage for the reduced loss of sanshool is not coherent as printed, so it is not repeated. A 60-day laboratory test.
Measured on the spice
Storage · Converts Hydroxy-α-sanshool, hydroxy-β-sanshool, hydroxy-ε-sanshool, pungency
Hydroxy-α-sanshool isolated from Zanthoxylum oleoresin decreased rapidly under UVB light, following second-order kinetics. The contents of hydroxy-α-, hydroxy-β- and hydroxy-ε-sanshool all changed on exposure, and a new compound formed that shares their mass and a similar structure; the authors show that the sanshools undergo isomerisation under UVB.
Conditions: in laboratory solvent · Three sanshools isolated from Zanthoxylum oleoresin and exposed to UVB light in different solvents
What this does not show: Read in the abstract only. Pure compounds in solvents under a UVB lamp, not husks of Sichuan pepper in a jar; it identifies light as a route of loss and gives no rate that applies to the spice.
Measured on the pure compound
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Piperine
Sichuan pepper is not botanically a pepper, contains no piperine, and does not produce heat. It is a citrus relative, and every part of the resemblance is in the English name.
Capsaicin
Frequently sold and described together because Sichuan cooking uses them together. The pairing is a culinary tradition built on the fact that the sensations are different, not evidence that they are similar.
Questions this page answers
- what is hydroxy-α-sanshool
- what does hydroxy-α-sanshool do
- which spices contain hydroxy-α-sanshool
- what is sanshool
- what is sanshools