Imagine yourself on the set of an old action movie. You’re watching the filming of a barroom brawl. Chairs slide across the bar, breaking glasses and bottles. More glass shatters against the wall. The extras begin hitting each other over the head with bottles. In the midst of the chaos, the director calls for the stunt man to fall through a window. The scene is set. The actors grab each other, struggle a little, and one is catapulted through the window. He rolls to the other side while shards of glass fall around his wincing face.
"Cut!" The stunt man gets up, brushes himself off, picks up a sharp-looking piece of the former window, begins chewing on it and asks, "When’s lunch? I’m starving!"
In the early days of motion pictures, sugar was the main ingredient of false glass. It was called "candy glass," and it was safer than real glass because it broke easily into what appeared to be dangerously sharp pieces. In reality, candy glass was much less sharp than real broken glass. It was made by dissolving sugar in boiling water to make a syrup, which was poured into a flat pan for each pane of glass. Since then, candy glass has been replaced by special thin plastics and paraffin wax. Even though sugar may no longer be a movie star, its resemblance to glass and our ability to manipulate its fascinating properties live on.
Culinary specialists trained in the art of sugar blowing use an intricate process of heating, cooling, and reheating sugar mixtures to create bowls, vases, fruit, swans—virtually anything that a glass blower can make. They prepare a basic recipe of hard candy, which is solid at room temperature. Using heat lamps, they heat the solid mixture until it softens, and then attach a soft ball of candy to a blow pipe. By carefully blowing through the pipe, they enlarge the air chamber inside the candy and control the outer shape with their fingers. While you may not have a complete sugar studio at home, you can observe the amazing properties of sugar by making candy.
Sugars are composed of relatively simple molecules. Identical sugar molecules stack tightly together to form crystals and are solid at room temperature, like table sugar. In a mixture of various types of sugar molecules, the stacking pattern is disrupted because the molecules are not shaped alike and cannot fit together as easily. These mixtures, such as honey and syrups, tend to be liquids at room temperature.
In making the peanut brittle shown here, you begin by mixing sugar, water and corn syrup. Notice the sugar crystals settling at the bottom of the pot. Heat disrupts the crystal structures, causing the sugar to dissolve in the water. The heated molecules move faster and become farther apart, enabling the solution to dissolve more and more sugar molecules, until it boils. Once the solution boils, many water molecules are released into the air, concentrating the solution and raising the boiling point. When the solution has dissolved all of the sugar that it can take, it is "saturated." Now the solution has a delicate balance of just enough sugar molecules and just enough heat to keep them dissolved. A disruption in the heat or the introduction of any foreign particle—even dust—can make the solution suddenly "supersaturated," which will cause it to recrystallize prematurely.
The secret to candy making is to control this process. Candies such as fudge are extremely supersaturated when cooling to room temperature and must be stirred or aerated continually to break large crystals into tiny fragments. This gives the fudge a velvety texture.
As early as the 1700s, people began documenting the different properties of sugar solutions at various concentration levels, creating the now familiar "thread-ball-crack" test. Confectioners predict the sugar concentration and boiling point by dropping a small amount of sugar solution into cold water and observing its behavior.
sugar behavior when dropped
concentration into cold water boiling point
80% forms a soft ball 240 degrees Fahrenheit/116 degrees Celsius
90% forms a hard ball 255 degrees Fahrenheit/125 degrees Celsius
98–99% forms hard ball that cracks 300 degrees Fahrenheit/150 degrees Celsius
The peanut brittle in this recipe is heat tested twice; once to the soft ball stage to add ingredients, and then to the hard crack stage. You cool it very quickly by pouring it into a large flat pan. Brittles can be made as plain or as elegant as you wish by replacing the peanuts with more exotic mixes of nuts. The candy ingredients are the same as those in caramels or taffies, which give them the dark brown color and buttery flavor. However, brittles are cooked to 300_F, the highest boiling point before burning, leaving an extremely low 1–2 percent moisture content. The result is a crunchy, crackable—brittle—confection.
Lynn Parrucci is program coordinator at Carnegie Science Center’s Kitchen
Theater. Jeff Jordan, education coordinator of the science theaters, contributed
to this article.
|1.5 teaspoon baking soda|
|1 teaspoon water|
|1 teaspoon vanilla|
|1.5 cups sugar|
|1 cup water|
|1 cup light corn syrup|
|3 tablespoons margarine or butter|
|1 pound shelled, unroasted peanuts|
Butter 2 cookie sheets, 15.5 x 12 inches; keep warm. Mix baking soda, 1 teaspoon water and the vanilla; reserve. Mix sugar, 1 cup water and the corn syrup in 3-quart saucepan. Cook over medium heat, stirring occasionally, to 240 degrees Fahrenheit on candy thermometer (or until small amount of mixture dropped into very cold water forms a soft ball that flattens when removed from water). Stir in margarine and peanuts. Cook, stirring constantly, to 300 degrees Fahrenheit (or until small amount of mixture dropped into very cold water separates into threads that are hard and brittle. Watch carefully so the mixture does not burn. Immediately remove from heat; stir in baking soda mixture. Pour half of the candy mixture onto each cookie sheet and quickly spread to about 1/4 inch thick; cool. Break into pieces. About 6 dozen candies.
Recipe from the Betty Crocker Cookbook.
Visit the Kitchen Theater at Carnegie Science Center to learn more about
the science of cooking, and get a taste of what we’re cooking and a recipe
to take home. For a schedule of daily cooking shows, check the schedule
board in the Science Center lobby on the day of your visit, or call 237-3400.
Be sure to ask if there is a guest chef appearing.