Saturation Science

• Traditional fudge recipes begin with bringing sugar and milk to a boil. The high heat of the boiling liquid allows more of the sugar’s molecules to dissolve until the liquid reaches what is known as its saturation point, meaning it can't absorb any more sugar. Fudge recipes calling for boiled sugar are calculated based on the saturation rate of granulated sugar, not powdered. While powdered sugar does dissolve in cold liquids, it contains up to 3 percent cornstarch, which can thicken the fudge and turn it lumpy.

Common Mistakes in Crystallization

• If temperatures are not quite high enough during the sugar boiling, not all the sugar will dissolve. This causes a problem later because even one tiny un-dissolved sugar granule can wreck a batch of fudge, causing it to crystallize and turn grainy. Another common mistake is leaving sugar granules on the sides of the pot during boiling. Fudge recipes using powdered sugar call for the liquid and fat to be cooked separately before adding the sugar. The powdered sugar is stirred in once the other ingredients have been melted and combined, so no candy thermometers are required to calculate saturation or crystallization.

Setting the Fudge

• What to do with the fudge once the ingredients have been cooked and combined depends on which method of fudge making you use. For traditional sugar-boiled recipes, a technique known as kneading prevents the fudge from becoming too soft or sticky. Allow fudge to cool slowly to 110 degrees Fahrenheit, then stir or whip the fudge to break down any sugar crystals that are beginning to form. This encourages a smooth, creamy texture as the fudge sets. When making fudge with powdered sugar, no kneading is required, because crystallization didn’t occur. Instead, allow the fudge to set by chilling the pan in the refrigerator.

Mix-in Magic

• Legend has it that See’s Candy Makers were the first to stir a mysterious ingredient into their fudge, now commonly known as marshmallow crème. Adding nuts, dried fruits and marshmallow bits to fudge adds personality and color to your candy without affecting the chemistry of your fudge. However, other ingredient substitutions can negatively affect the outcome of cooked fudge. For best results, don’t double the ingredients to make a larger batch; instead, make two smaller batches. Use the exact measurements called for in the recipe, and don’t substitute other fats when the recipe calls for butter.