On Food and Cooking

chemicals. One group, the thiocyanates, are
formed in mustard plants and their relatives,
horseradish and wasabi, when the plant cells
are damaged. Most thiocyanates are small,
light, water-repelling molecules — a dozen or
two atoms — that readily escape from the
food into the air in our mouth, and up our
nasal passages. In both the mouth and nose
they stimulate nerve endings that then send a
pain message to the brain. The second group
of pungent chemicals, the alkyl-amides, are
found preformed in a number of unrelated
plants, including the chilli, black pepper,
ginger, and Sichuan pepper. These molecules
are larger and heavier — 40 or 50 atoms —
and therefore less prone to escape the food
and get up our nose; they mostly affect the
mouth. And their action turns out to be very
specific. They bind to particular receptors on
certain sensory nerves and essentially cause
those nerves to become hypersensitive to
ordinary sensations — and thus to register the