On Food and Cooking

The first factor that influences candy texture
is the concentration of sugar in the cooked
syrup. Confectioners have found from long
experience that certain syrup concentrations
are best for making certain kinds of candy.
Generally, the more water the syrup contains,
the softer the final product will be. So the
cook must know how to make and recognize
particular syrup concentrations. This turns out
to be pretty simple. When we dissolve sugar
or salt in water, the boiling point of the
solution becomes higher than the boiling point
of pure water (see p. 785). This increase in the
boiling point depends predictably on the
amount of material dissolved: the more
dissolved molecules in the water, the higher
the boiling point. So the boiling point of a
solution is an indicator of the concentration of
the dissolved material. The graph in the box
below shows, for example, that a sugar syrup
that boils at 250ºF/125ºC is about 90% sugar
by weight.