Hard-crack stage

According to the Exploratorium, hard-crack stage happens at 300 to 310 degrees Fahrenheit, when the syrup is about 99 percent sugar. Syrup dropped into cold water forms hard, brittle threads that break when bent.

Nearly no water remains, so the cooled candy sets glassy and hard. The museum lists toffee, nut brittles and lollipops among the sweets made at this stage.

Cooks check the stage with a candy thermometer or a cold-water test, and the syrup must be watched closely because it moves quickly toward caramel color just beyond this point. The listed temperatures are for sea level; at altitude the page says to subtract 1 degree Fahrenheit for every 500 feet above sea level.

It follows soft crack and comes just before the caramel stages, which begin around 320 degrees Fahrenheit, when the sugar liquefies completely and begins to color.