The Science of Candy: Sugar Chemistry -
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The National Confectioners Association offers tips for safely enjoying Halloween 2021 from a distance1 and at home2. Although the way we celebrate Halloween may be different than years past, one thing that will remain constant is the candy.

What is Candy Made Of?

The primary ingredient in most candies is sugar.3 Sugar is a general term used to describe a class of molecules that includes sucrose, as well as fructose and glucose.

How is Candy Made?

The first step to making most candies is typically to dissolve sugar into boiling water. This forms a sugar syrup that can be cooled by removing it from the burner. However, the way the syrup is cooled determines the type of candy produced.4 For example, rock candy is made by allowing the sugar syrup to cool over several days, while fudge requires continuous stirring of the cooling syrup so that the sugar crystals that form remain small.

Types of Sugar Chemistry

The two main categories of candy, crystalline and non-crystalline, result from the arrangement of sucrose molecules in the candy.

Crystalline Candy

Crystalline candy, such as fudge and fondant, normally has a lower sugar concentration than non-crystalline candy and may contain small fine crystals of sucrose.

Science of Fudge: How Fudge Is Made

Fudge is made by heating sugar and water to a temperature above the boiling point for water, which is 212° Fahrenheit.4 The candy maker pours the syrup into a pan so it can cool faster; this technique helps prevent sucrose molecules from forming into a large crystal. Once cooled to 122° F, the syrup is stirred and scraped, forming many crystals at once. Continued stirring helps the sucrose molecules spread among and bind to the crystal seeds. This helps keep the size of the crystals small and creates the fudge’s milky texture.

Non-Crystalline Candy (Amorphous)

Glass candy, cotton candy and gummies are examples of non-crystalline candy, which generally has a higher sugar concentration than crystalline candy.4

Science of Rock Candy and Glass Candy

To make glass candy, sugar syrup is cooled rapidly to prevent crystals from forming. The dissolved sucrose molecules bind with one another, which causes the candy to become amorphous and take on the appearance of glass.

Fun fact:  glass candy was historically used for stunts that involved people breaking windows.  Gummies are made in a similar way to glass candy, but with gelatin added to the sugar syrup to give it a rubbery consistency.

Other common candy ingredients

While sugar is typically the primary ingredient in candy, many candies also include preservatives and other ingredients to keep treats sweet and edible. For example, the University of Hawaii’s Food Safety and Technology newsletter article, Common Food Additives in Candy,5 identifies several candy additives, including the following:

  • Butylated hydroxyanisole (BHA) – An antioxidant that prevents fats and oils from becoming rancid in candies such as peanut-butter cups.
  • Gum base – One of the main ingredients in chewing gum, it’s made by blending and heating several vegetable or synthetic fibers with a softener such as paraffin and antioxidants.
  • Potassium sorbate – A preservative that is the potassium salt of sorbic acid,6 which is also a preservative.

Other common ingredients in candy can include caffeine7, ascorbic acid and citric acid, which gives candies like lemon drops their tart flavor.

For more information about candy and its chemistry, see these resources:


National Confectioners Association

STEAM Powered Family: Candy Science


1Halloween 2021: Fun From a Distance – Always a treat

2Halloween 2021: At Home Celebrations – Always a treat

3National Chemistry Week: The Chemistry of Candy – Compound Interest (

4American Chemical Society:  The Sweet Science of Candymaking

5University of Hawaii:  Common food additives in candy (

6National Library of Medicine:  Food applications of sorbic acid and its salts – PubMed (

7National Confectioners Association:  Unwrap the Facts – Always a treat