On Food and Cooking

in about 30 seconds. A piston or spring or
electrical pump drives 200ºF/93ºC water
through finely ground coffee at 9 atmospheres
of pressure. (Inexpensive household machines
rely on excessively hot steam, develop far less
pressure, and take longer to brew, so the result
is relatively thin and harsh.) The proportion of
ground coffee is three to four times the
amount used in unpressurized brewing, and
deposits three to four times the concentration
of coffee materials in the brew, creating a
substantial, velvety body and intense flavor.
These extracted materials include a relatively
large amount of coffee oils, which the high
pressure forces from the bean particles to
form a creamy emulsion of tiny droplets, and
which contribute to the slow, prolonged
release of coffee flavor in the mouth, long
after the last sip. Another unique feature of
espresso is the crema, the remarkably stable,
creamy foam that develops from the brew and
covers its surface. It’s the product of carbon