Sugar Temperatures - NoBadFoodLab

Stage - Temp - Sugar Concentration
Thread (Syrup) - 110 to 112 °C (230 to 234 °F) - 80% Sugar Concentration
Soft Ball (Fudge) - 112 to 116 °C (234 to 241 °F) - 85% Sugar Concentration
Firm Ball (Soft Caramel Candy) - 118 to 120 °C (244 to 248 °F) - 87% Sugar Concentration
Hard Ball (Nougat) - 121 to 130 °C (250 to 266 °F) - 90% Sugar Concentration
Soft Crack (Salt Water Taffy) - 132 to 143 °C (270 to 289 °F) - 95% Sugar Concentration
Hard Crack (Toffee) - 146 to 154 °C (295 to 309 °F) - 99% Sugar Concentration
Clear Liquid - 160 °C (320 °F) - 100% Sugar Concentration
Brown Liquid (Liquid Caramel) - 170 °C (338 °F) - 100% Sugar Concentration
Burnt Sugar - 177 °C (351 °F) - 100% Sugar Concentration

The names come from the methods used to test the syrup before thermometers became affordable. The "thread" stage is tested by cooling a little syrup, and pulling it between the thumb and forefinger. When the correct stage is reached, a thread will form. This stage is used for making syrups. For subsequent stages, a small spoonful of syrup is dropped into cold water, and the characteristics of the resulting lump are evaluated to determine the concentration of the syrup. A smooth lump indicates "ball" stages, with the corresponding hardness described. At the "soft crack" stage, the syrup forms threads that are just pliable. At the "hard crack" stage, the threads are brittle.

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 171 °C (340 °F) or higher, the sucrose molecules break down into many simpler sugars, creating an amber-colored substance known as caramel. This should not be confused with caramel candy, although it is the candy's main flavoring.