Heat and Numbing.
A habanero is about fifty times hotter than a jalapeño. Water spreads the fire; a sip of whole milk takes it away.
Pungency is not a taste but a touch. Capsaicin in chillies switches on TRPV1, the receptor that warns of heat above about 43 °C, so the mouth reports burning when nothing is hot. Piperine in black pepper does something similar, more gently. Allyl isothiocyanate in mustard, horseradish and wasabi is volatile and rushes up the nose. And hydroxy-α-sanshool in Sichuan pepper (花椒) excites touch nerves, producing a buzzing, tingling numbness — 麻 — that pairs with chilli's 辣 in Sichuan cooking.
Chilli heat is measured in Scoville heat units (SHU): how many times an extract must be diluted before tasters stop noticing it; one part per million of capsaicin is about 16 SHU. Capsaicin is oily — it dissolves in fat and alcohol, hardly at all in water — which is why water spreads the burn round the mouth and whole milk, yoghurt or a fatty dish soothes it. The workshop measures the heat of a dish.
Below: the heat of a dish, in Scoville units, against the chilli you put in for four chillies, with mild-to-fiery bands, and the share of capsaicin that a sip of milk of different fat contents takes into its fat (published Scoville ranges; partition from capsaicin's log P of about 3).
- Explain why chilli feels hot.
- Estimate the heat of a dish from the chilli in it.
- Explain why milk soothes chilli and water does not.
- Distinguish 麻 from 辣.
Measure the fire, choose the cure
Three grams of jalapeño in a 600 g dish gives about 25 SHU, barely warm; three grams of habanero, about 1,125 SHU — fiery, 45 times hotter for the same weight. Heat also varies within a chilli: most capsaicin sits in the pale ribs (placenta) holding the seeds, so removing them tames it, and the same variety varies with sun, water and ripeness. Add chilli in steps and taste; heat is easy to add and hard to take away.
To cool a burning mouth, drink something with fat: whole milk takes about 98 % of the capsaicin it meets into its fat in this model, cream nearly all, water none — water just spreads it. Sugar and acid help a little; time helps most. In cooking, chillies fried in oil (辣椒油, chilli oil) give their capsaicin and colour to the oil, which carries it through the dish. Sichuan pepper's 麻 is a different sense entirely: its sanshool makes the lips feel a vibration of about 50 per second, and it is toasted lightly and ground fresh because the tingle fades in storage.
Taste a crumb of chilli, then sip water: the burn spreads. Taste another and sip whole milk or eat a spoon of yoghurt: it fades. Then chew a single Sichuan peppercorn and notice that the buzzing is not heat at all.
Terms
- Capsaicin
- The compound in chillies that triggers the body's heat-pain receptor.
- Scoville heat unit
- A measure of chilli heat: the dilution at which it can no longer be noticed.
- 麻
- The tingling numbness of Sichuan pepper.
- 辣
- The burning heat of chilli.
Sources
- One part per million of capsaicin corresponds to about 16 Scoville heat units (the conversion used with HPLC measurements, ASTA method 21.3).
- Scoville heat of chillies (published ranges): bell pepper 0, jalapeño 2 500–8 000, cayenne 30 000–50 000, Thai bird's eye 50 000–100 000, habanero 100 000–350 000 SHU; pure capsaicin about 16 000 000 SHU.
- N. Hagura, H. Barber and P. Haggard, "Food vibrations: Asian spice sets lips trembling", Proceedings of the Royal Society B 280: 20131680 (2013): the tingle of Sichuan pepper matches a vibration of about 50 Hz.
- NIST Chemistry WebBook (SRD 69): normal boiling points and enthalpies of vaporisation; octanol–water partition coefficients (log P) from PubChem. Vapour pressure from the Clausius–Clapeyron equation.