the help of the steam nozzle on an espresso
coffee machine. Steaming milk accomplishes
two essential things simultaneously: it
introduces bubbles into the milk, and it heats
the bubbles enough to unfold and coagulate
the whey proteins into a stabilizing web.
Steam itself does not make bubbles: it is
water vapor, and simply condenses into the
colder water of the milk. Steam makes
bubbles by splashing milk and air together,
and it does this most efficiently when the
nozzle is just below the milk surface.
One factor that makes steaming tricky is
that very hot milk doesn’t hold its foam well.
A foam collapses when gravity pulls the
liquid out of the bubble walls, and the hotter
the liquid, the faster it drains. So you have to
use a large enough volume of cold milk — at
least ^2 / 3 cup/150 ml — to make sure that the
milk doesn’t heat up too fast and become too
runny before the foam forms.
Cream