When we say a dish is “spicy”, we usually mean that it tastes “hot”. The term “spicy”, though, covers far more than that. It includes chillies, peppercorns, ginger, mustard, horseradish, and many other stimulating foods.
Chillies bring an unmistakable, “my mouth is burning” heat that many find delightful, if an ordeal at times”. What about the unassuming chilli sets our mouths aflame?
Chilli has a special something that other spices don’t: capsaicin. A chemical irritant, capsaicin bonds with the mouth’s temperature receptors, causing us to feel excessive heat. Other hot spices’ active components act differently. Just look at the mustard family—its more volatile substance wafts up the nose instead, as anyone who has felt wasabi’s nasal punch can attest.
Eaten on its own, a chilli’s “hotness” comes down to its capsaicin concentration, measured in terms of Scoville heat units (SHU). Although some have estimated other “hot spices” in SHU terms, their heat pales in comparison. Pepper’s and ginger’s pure components are estimated at 100,000 and 60,000 SHU, respectively, but pure capsaicin comes in at 16 million SHU.
Within chilli varieties, the range of heat is astounding. The world’s hottest verified pepper—the Carolina Reaper—is 24 times hotter than the mighty bird’s eye chilli, an iconic chilli in Asian cuisine.