The final texture of candy depends on the sugar concentration. As the syrup is heated, it boils, water evaporates, the sugar concentration increases, and the boiling point rises. A given temperature corresponds to a particular sugar concentration. In general, higher temperatures and greater sugar concentrations result in hard, brittle candies, and lower temperatures result in softer candies. These "stages" of sugar cooking are:
|Stage||Temperature in °F||Temperature in °C||Sugar concentration|
|soft ball (e.g., fudge)||234-240°F||112-115°C||85%|
|hard crack (e.g., toffee)||295-310°F||146-154°C||99%|
|brown liquid (caramel)||338°F||170°C||100%|
The names come from the process used to test the syrup before thermometers became affordable: a small spoonful of syrup was dropped into cold water, and the characteristics of the resulting lump were evaluated to determine the concentration of the syrup. Long strings of hardened sugar indicate "Thread" stage, while a smooth lump indicates "ball" stages, with the corresponding hardness described. The "crack" stages are indicated by a ball of candy so brittle that the rapid cooling from the water literally causes it to crack.
This method is still used today in some kitchens. A candy thermometer is more convenient, but has the drawback of not automatically adjusting for local conditions such as altitude, as the cold water test does.
Once the syrup reaches 340°F or higher, the sucrose molecules break down into many simpler sugars, creating an amber-coloured substance known as caramel. This should not be confused with caramel candy, although it is the candy's main flavouring.