Hard Candy: from Hard Crack to the Glass Transition Careful control over formulation and processing conditions is required to produce quality hard candy with good shelf life. Richard W. Hartel, PhD University of Wisconsin–Madison H Richard Hartel is a professor of food engineering in the Food Science department at the University of Wisconsin – Madison. He also is course coordinator for the two-week Resident Course in Candy Technology held annually in Madison. ard candy is produced by boiling a sugar syrup to the hard crack temperature which, on a candy thermometer, is about 149°C (300°F). At hard crack, water content is low and the sugar mass is extremely viscous. After flavoring, the candy mass is either deposited into molds or cooled to a highly plastic state that can be easily formed into desirable shapes. Upon cooling to room temperature, the piece sets into a sugar glass that, if protected from heat and humidity, retains its quality for years. After touching on the basics behind hard candy manufacture, this review will discuss the numerous chemical and physical changes that occur in the sugar mass during the manufacturing process that can potentially influence finished-product characteristics and quality. INTRODUCTION Hard candies (also known as high-boiled sweets) come in a wide variety of sizes, flavors and shapes — from root beer barrels to lollipops. To make hard candy, a sugar syrup is cooked to hard crack temperature (145°– 152°C; 295°– 305°F) to reduce water content to 1 to 3 percent. When cooled to room temperature, the highly viscous candy 70 September 2012 • The Manufacturing Confectioner mass turns into a sugar glass with very low molecular mobility. It is this low mobility that provides the long stability and shelf life of hard candy, as long as proper storage conditions (cool and dry) are maintained. Besides flavor and color, hard candy formulations vary primarily in their saccharide profile, with the ratio of sucrose to glucose syrup solids varying from as high as 80:20 down to about 30:70 (although a more common range might be 60:40 to 40:60), as seen in Figure 1. A typical reducing sugar target is 16 to Typical Compositions (in %) of Fiinished Hard Candy High Sucrose Medium Sucrose Low Sucrose Sucrose 70 – 80 50 – 60 30 – 40 Glucose 20 – 30 40 – 50 60– 70 syrup solids Acid 0–2 0–2 0–2 0.2 – 0.3 0.2 – 0.3 0.2 – 0.3 Flavor1 Color 0.01 – 0.02 0.01 – 0.02 0.01 – 0.02 Water 2–4 2–4 2–4 Reducing 8.4–12.6 16.8 – 21.0 25.2 – 29.4 sugar levels2 1-Flavor levels vary widely depending on flavor activity and consumer preferences. 2-Based on 42 DE glucose syrup solids; calculated as DE of glucose syrup times fractional level of glucose syrup content (e.g., 42 times 30% gives 12.6). Figure 1 ➤