On Food and Cooking

first concentrated by evaporation, and then
table sugar is added to give a total sugar
concentration of about 55%. Microbes can’t
grow at this osmotic pressure, so sterilization
is unnecessary. The high concentration of
sugars causes the milk’s lactose to crystallize,
and this is controlled by seeding the milk with
preformed lactose crystals to keep the crystals
small and inconspicuous on the tongue (large,
sandy lactose crystals are sometimes
encountered as a quality defect). Sweetened
condensed milk has a milder, less “cooked”
flavor than evaporated milk, a lighter color,
and the consistency of a thick syrup.
Powdered or dry milk is the result of taking
evaporation to the extreme. Milk is
pasteurized at a high temperature; then about
90% of its water is removed by vacuum
evaporation, and the remaining 10% in a spray
drier (the concentrated milk is misted into a
chamber of hot air, where the milk droplets
quickly dry into tiny particles of milk solids).