Hard Candies

Hard candies are made the same way as caramel by boiling sugar mixtures. Normally taste substances—for example, fruit extracts, nuts, or licorice-are added to the mixture, but not cream. The boiling point for the mixture depends on the water content; it rises as the water evaporates.

Hard candies are formed when a sugar mixture that has lost 99 percent of its water content is cooled suddenly so that it is trapped in a glass state. The hardness and fragility of the candies depends on the glass-transition temperature of the sugars being used. These can be quite different: 41°F (5°C) for fructose, 88°F (31°C) for glucose (grape sugar), and 144°F (62°C) for sucrose (ordinary sugar). The glasstransition temperature can be determined reasonably accurately by using a weighted average of the glass-transition temperatures of the sugars in the mixture. Below this temperature, the melted sugar will harden and become a glass. Consequently, mixtures containing a sugar with a very low glass-transition temperature will turn to glass at a lower temperature, resulting in a more plastic substance.