This syrup is essentially corn syrup of higher concentration. It contains only 15 to 19.7 percent water. Glucose is one of the basic ingredients in rolled fondant. It is available in cake decorating and baking supply stores. A close approximation can be made using corn syrup: Bring 1 cup of corn syrup to a full boil. Remove it from the heat and cool completely. Stir in 1/2 cup of unheated corn syrup. Glucose is highly prone to fermentation, resulting in small bubbles and a sour taste. It will keep indefinitely if stored airtight, refrigerated, and not contaminated by a spoon that has been used for other substances, including water.