Reference point
Toast a few mắc khén berries in a dry pan and smell as soon as they become fragrant.
Do this before you read on. An entry only works when you have just smelled the thing.
Zesty, bright, with a clear citrus-peel note and a layer of wood behind. It is not hot like black pepper; it numbs the tip of the tongue.
The citrus note is the surprise. Prickly ash is not a citrus, yet it gives that impression so strongly that many people describe it as “lemon pepper”.
The numbing is a phenomenon of its own, neither a smell nor a taste.
How to smell it
Dry-toast it in a pan until just fragrant, then turn off the heat at once — too much heat and all the brightness is lost. Smell the freshly toasted berries, then pound them and smell again. Then taste a little to feel the numbing.
Why this one is hard
Because the numbing dominates the experience and makes people forget to analyse the smell. To smell it properly, smell before you taste.
Don’t confuse with
This entry
Prickly ash pepper
Spicy family
Prickly ash pepper has a citrus-peel note and numbs the tongue; black pepper has a dry woody note and is hot. Two different nerve mechanisms.
Scientific note
The numbing comes from hydroxy-alpha-sanshool, an amide that acts not on the heat or pain receptors but on a group of rapidly adapting touch receptors — the same ones that detect light vibration on the skin. Research has measured the frequency people perceive at about 50 hertz, that is, fifty times a second. In other words it is neither taste nor smell: it is a sensation of touch with nothing touching you. It is a completely different mechanism from the capsaicin in chilli. The citrus smell, on the other hand, comes from limonene and other monoterpenes in the husk.
In Vietnamese life
Mắc khén is a base spice of Thai and Muong cooking in the northwest, essential in chẩm chéo dipping sauce and in meat smoked over the kitchen fire. It has become widely known to the majority Kinh population only in the last twenty years or so.