A hard candy (American) or boiled sweet (British), is a sugar candy prepared from one or more sugar-based syrups that is heated to a temperature of 160 °C (320 °F) to make candy.
Among the many hard candy varieties are stick candy such as the candy cane, lollipops, rock, aniseed twists, and bêtises de Cambrai. "Boiled" is a misnomer, as sucrose (a disaccharide) melts fully at approximately 186 °C. Further heating breaks it into glucose and fructose molecules before it can vaporize.
Most hard candy is nearly 100% sugar by weight, with a tiny amount of other ingredients for color or flavor, and negligible water content in the final product. Recipes for hard candy may use syrups of sucrose, glucose, fructose or other sugars. Sugar-free versions have also been created.
Recipes for hard candy use a sugar syrup, such as sucrose, glucose or fructose. This is heated to a particular temperature, at which point the candy maker removes it from the heat source and may add citric acid, food dye, and some flavoring, such as a plant extract, or essential oil. The syrup concoction, which is now very thick, can be poured into a mold or tray to cool, or a cooling table in case of industrial mass production. When the syrup is cool enough to handle, it can be folded, rolled, or molded into the shapes desired. After the boiled syrup cools, it is called hard candy, since it becomes stiff and brittle as it approaches room temperature.
Chemistry
Chemically, sugar candies are broadly divided into two groups: crystalline candies and amorphous candies. Crystalline candies are not as hard as crystals of the mineral variety, but derive their name and their texture from their microscopically organized sugar structure, formed through a process of crystallization, which makes them easy to bite or cut into. Amorphous candies have a disorganized crystalline structure. Hard candies are non-crystalline, amorphous candies containing about 98% (or more) solid sugar.