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