Quite simply it’s a flowing mixture of sugar and usually at
least a little water. That water is partly responsible for the
fact that most syrups, despite their sugar concentration, don’t
crystallize easily. But there’s usually something else in there
that inhibits crystallization, a little something called invert
sugar. Invert sugar is a term that gets tossed around quite a
bit in cooking and baking circles, about as much as
“caramelization” and “Maillard reaction.” But what is it
exactly? Basically, invert sugar is a mixture of sucrose (25%)
and its two component sugars, glucose and fructose (75%). Invert
sugar exists in nature but is usually made by humans for various
culinary and scientific applications. You get it by making a
mixture of sucrose (table sugar) and water, then heating it and
adding an acid. In the kitchen that acid can be lemon juice,
tartaric acid, vinegar or any number of others. The effect of
heat and acid on sucrose is that it splits the molecule into the
above mentioned mixture, and onc