Hard Candy: from Hard Crack to the Glass Transition

Hard Candy: from Hard
Crack to the Glass
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
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.
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
70 – 80
50 – 60
30 – 40
20 – 30
40 – 50
60– 70
syrup solids
0.2 – 0.3
0.2 – 0.3
0.2 – 0.3
0.01 – 0.02 0.01 – 0.02 0.01 – 0.02
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