Temperature determines sugar structure from liquid to glass
As sugar syrups heat, water evaporates and sugar concentration rises. At low temperatures (110-113C), dissolved sugar remains pliable after cooling, forming the soft ball stage. Higher heat (121-130C) creates the hard ball, which cracks under your teeth. Beyond 149C, sugar enters the hard crack stage, forming brittle shards. Above 160C, sugar caramelizes, developing brown color and bitter-sweet flavor.
The stages represent different crystal structures and water content. Soft ball still contains enough water to form a soft solid at room temperature. Hard ball has less water and cannot fold or bend. Hard crack has almost no water, becoming glassy and snap-brittle.
Each stage suits different candy applications
Soft ball stage is used for fudge, caramels, and fondant fillings because it remains pliable enough to work with. Hard ball is the target for lollipops and brittles that should hold their shape rigidly. Hard crack creates boiled sweets, rock candy, and pralines. Caramel takes the sugar past the color thresholds into deeper flavor territory, used for sauces, dessert glazes, and decorative poured sugar.