On Food and Cooking

by “hot” spices and vegetables — chillis,
black pepper, ginger, mustard, horse-radish,
onions, and garlic — are most accurately
described as irritation and pain (for why we
can enjoy such sensations, seep. 394). The
active ingredients in all of these are chemical
defenses that are meant to annoy and repel
animal attackers. Very reactive sulfur
compounds in the mustard and onion families
apparently do mild damage to the unprotected
cell membranes in our mouth and nasal
passages, and thus cause pain. The pungent
principles of the peppers and ginger, and some
of the mustard compounds, work differently;
they bind to a specific receptor on the cell
membranes, and the receptor then triggers
reactions in the cell that cause it to send a
pain signal to the brain. The mustard and
onion defenses are created only when tissue
damage mixes together normally separate
enzymes and their targets. Because enzymes
are inactivated by cooking temperatures,