October 19, 2014

The Science of Sugar

by Christine Hoekenga

With Halloween just around the corner, candy is on the brain. So it’s fitting that the American Chemical Society has chosen “The Sweet Side of Chemistry–Candy” as the theme for this year’s celebration of National Chemistry Week (October 19-25).

Colorful gum drops

Sucrose is a key ingredient in candies like these gum drops.

We all know that candy usually has a lot of “sugar” in it, but what does that really mean? Is the sugar in a chewy caramel the same as the sugar in a brittle lollipop? If so, why are the textures and consistencies of those two sweet treats so different?

The answers lie in chemistry.

The type of sugar people are usually most familiar with is sucrose (C12H22O11)–the white crystalline substance commonly used in baking or added by the spoonful to tea or coffee. Each sucrose molecule is actually a disaccharide (double sugar), consisting of two smaller sugar molecules bonded together: one glucose and one fructose.

When mixed with water and heated, sucrose crystals dissolve, forming a sugar syrup used in making candy. As the temperature of the syrup rises and water boils away, the concentration of the sugar increases, which affects the way the molecules behave when the syrup eventually cools. Confectioners (people who make candy) have described distinct stages for the syrup based on the highest temperature it reaches during cooking. They use these categories to make different types of sweets.

Diagram of a sucrose molecule

A sucrose molecule is composed of one glucose molecule (left) and one fructose molecule (right).

You may have seen the term “soft ball” in recipes for fudge or pralines or the term “hard crack” in toffee and peanut brittle recipes. These are just two of the temperature stages recognized in candy-making, and although they may seem like rough rules of thumb for home bakers, they actually have quite specific parameters that lead to specific results.

Soft ball stage, for example, is achieved when the sugar syrup has been heated to between 113° and 115°C. At that point, the sugar concentration will be reach about 85 percent, which is a good consistency for making fudge. The term soft ball (and the names of all the other temperature stages) comes from the “cold water test,” which allows a confectioner to test the temperature stage without a thermometer. At soft ball stage, when a small amount of the syrup is dropped into cold water, it will form a soft, flexible ball that will naturally flatten out after a few moments. Other stages include:

  • Firm ball (118°–120°C and 87 percent sugar), used in making marshmallows and caramels
  • Hard ball (120°–130°C and 92 percent sugar), used in making rock candy and gummies
  • Soft crack (132°–143°C and  95 percent sugar), used in making butterscotch and taffy
  • Hard crack (148°–155°C and 99 percent sugar), used in making lollipops and brittles
  • Clear liquid (160°-169° C and 100 percent sugar)
  • Brown liquid (170°-176° C and 100 percent sugar)–also known as caramelized sugar–used to flavor many deserts

Notice that caramels and sugar that has been caramelized are not the same. Caramels are the familiar chewy candy made from mixing sugar in the firm ball stage with cream and other ingredients, depending on the recipe. The brown color you see in caramels is the result of the Maillard Reaction–a complex chemical reaction that occurs when sugars (like sucrose, glucose or fructose) react with amino acids (like those found in cream) at an elevated temperature. The Maillard Reaction is responsible for colors, odors, and flavors in cooked foods of all kinds, from caramels to popcorn to steak.

The creamy texture of some candy fillings is the result chemistry.

Caramelized sugar, on the other hand, is pure sugar that has been heated to 170° C. At that temperature, the sucrose begins to break down and form other compounds. Even food chemists do not completely understand the chemical reactions that occur during the caramelization process, but the results are delicious. Caramelized sugar has complex flavors, ranging from nutty to buttery, and it’s used to give a rich taste to many desert items.

So next time your sweet tooth leads you to a gummy bear, a piece of fudge, or a lollipop, remember that the flavors and textures of those treats are no accident. They are the result of some seriously sweet chemistry.

Read more about sucrose, fructose and glucose in our Carbohydrates module

See pictures and videos of each temperature stage used in cold water test in the Exploratorium’s Science of Cooking exhibit

Learn about other tricks of chemistry that confectioners use to make the perfect candy in the Exploratorium’s Science of Cooking exhibit

Explore the history of the Maillard Reaction from its discovery in 1912 to modern research on its implications for food safety and health in Chemical and Engineering News

Watch a video from Food Science TV demonstrating the Maillard Reaction and the process of caramelization in the kitchen

Christine Hoekenga

Written by

Christine is a freelance writer, editor, and content strategist, specializing in science and nature. She holds an Bachelor's degree in Environmental Science and Media Studies and a Master's of Science Writing. She has been working in science communication and education for nearly a decade as a journalist, an organizer for conservation groups, and a museum educator. Before joining the Visionlearning team, she served as the New Media and Online Community Manager for the Webby award-winning Smithsonian Ocean Portal. Christine is assisting Visionlearning with developing new modules and glossary terms, managing the blog, and outreach through social media.

The views expressed above do not necessarily represent those of Visionlearning or our funding agencies.