Invert sugar is created by combining a sugar syrup with a small amount of acid (such as cream of tartar or lemon juice) and heating. This inverts, or breaks down, the sucrose into its two components, glucose and fructose, thereby reducing the size of the sugar crystals. Because of its fine crystal structure, invert sugar produces a smoother product and is used in making candies such as fondant, and some syrups. The process of making jams and jellies automatically produces invert sugar by combining the natural acid in the fruit with granulated sugar and heating the mixture. Invert sugar can usually be found in jars in cake-decorating supply shops.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.