When fondant is good, it’s good. Good fondant gives your cake a perfectly smooth and flawless finish.
If kept air tight, fondant lasts forever, but it starts to dry immediately when exposed to air and can be tricky to work with. Once your fondant is past its prime, there’s really nothing you can do to restore it to its formerly silky smooth state. However, while it will never be perfect, there are a few things you can try to make old, dry fondant workable again.
1. Glycerine. Glycerine is an ingredient in fondant that keeps it pliable and prevents it from drying out too quickly. (For a fascinating, scientific explanation of glycerine’s role in keeping fondant flexible, read this post on Joe Pastry’s blog.) Glycerine is a humectant (a moisture-retaining substance), so the molecules in glycerine bond with and trap water molecules, keeping your fondant moist (Source: Joe Pastry, 2008).
It’s one of those ingredients you can buy in a drug store (as a humectant, glycerine also keeps hair and skin moist) for a fraction of the price of a cake decorating store. If you’re willing to forgo the fancy branding you can get a quart-sized bottle of Essential Depot glycerine (below, left) on Amazon for $13.95; the 2-ounce bottle of Wilton glycerine (below, right) is around $5. At just .43 cents per ounce, the Essential Depot is a much better value than the $2.50 per ounce Wilton glycerine. Just be sure that if you buy glycerine that’s not specifically marketed for cakes it says “Food Grade”.
To use, simply knead a little glycerine in to your fondant. Begin with about a teaspoon per pound of fondant, and work quickly to knead it in. This will buy you some time before your fondant dries out, but not much. Re-roll and apply your fondant.
Glycerine can also be used on fondant that’s been rolled out and applied to a cake but has a dry cracked appearance, sometimes known as “elephant skin”. Gently rub glycerine onto the cracked fondant using the tips of your fingers, taking care not to rub through to the cake.
2. Shortening. Usually known by the brand name Crisco, hydrogenated vegetable oil (shortening) is 100% fat (as opposed to butter, which is about 80% fat). Kneading a small amount in to your fondant can make it smoother and easier to work with. Be very careful: adding too much can make your fondant heavy and stretchy. (If this happens, add additional corn starch or sifted confectioners sugar and knead in until the proper consistency is restored.) Shortening, like glycerine, can also be rubbed onto cracked fondant after the fondant has been applied to the cake to remove the appearance of elephant skin.
3. Food Processor. The food processor method works especially well for smaller pieces of fondant. Simply place a small amount of fondant into the bowl of your food processor and pulse. The blades of the food processor with heat and soften your fondant, making it easier to work with. (This is also a good method for coloring fondant: Just add your food coloring along with your fondant to the bowl of your food processor and pulse.) The food processor will most likely break your fondant up into small balls which can then be easily gathered and kneaded together. Be sure not to put rock hard pieces in the food processor. (I learned the hard way that this can cause irreparable damage to your food processor.)
4. Microwave. The microwave is the absolute last resort. If your fondant has become so dry that kneading becomes virtually impossible, 30 seconds or so in the microwave will heat it enough to make it kneadable again. (Do test your microwave first using 10 second intervals.) However, this is a one shot deal. You have to work quickly to roll out your fondant and cover the cake, for once microwaved and the fondant cools down, your fondant will become even drier–almost crumbly–and cannot be used again.