On Food and Cooking

metallic state. For this reason it was the first
metal to be used in tool making, about 10,000
years ago. In the kitchen, it is prized for its
unmatched conductivity, which makes fast
and even heating a simple matter. But copper
is also relatively expensive, since its
conductivity has made it the preferred
material for millions of miles of electrical
circuitry. It is troublesome to keep polished,
because it has a high affinity for oxygen and
sulfur, and forms a greenish coating when
exposed to air. Most important, copper
cookware can be harmful. Its oxide coating is
sometimes porous and powdery, and copper
ions are easily leached into food solutions.
Copper ions can have useful effects: they
stabilize foamed egg whites (p. 102), and the
green color of cooked vegetables is improved
by their presence. But the human body can
excrete copper in only limited amounts, and
excessive intake may cause gastrointestinal
problems and, in more extreme cases, liver