Crystallization of sugar

Crystallized sugar looks like damp, white sand. It happened often as a result of not being properly melted during cooking. If even one sugar crystal comes into contact with cooked syrup, it can start a chain reaction that turns the whole thing into a mass of sugar crystals.

Crystallization can occur when granulated particles of sugar come in contact with melted particles, or when the melted sugar is agitated too much during cooking.

This can be controlled by a process called inversion. Inversion is a chemical change to regular sugar into another form of sugar that resists crystallizing.

If an acid, such as cream of tartar or lemon juice, is added to a syrup before or during cooking, some of the sugar is inverted. Glucose or corn syrup may also be added to control crystallization in boiling syrup. 

Crystallization also may be prevented by brushing down the sides of the pan with water during the cooking process.

Sugar is purposely crystallized during the cooking process for crystalline confections like fondants and fudge because controlled crystallization forms thousands of microscopic sugar crystals that create smooth and creamy texture.

Conversely, crystallization must be avoided during the production of non-crystalline confections such as caramels, hard candies and toffees.
Crystallization of sugar