Science of Candy: What's Special About Fudge? | Exploratorium (2024)
Whats special about fudge?
Fudge is one of the rare exceptions to the rule that sugar crystals are not desirable in candy. Tiny microcrystals in fudge are what give it its firm texture. The crystals are small enough, however, that they dont feel grainy on your tongue, but smooth.
While you ultimately want crystals to form, it's important that they don't form too early. The key to successful, nongrainy fudge is in the cooling, not the cooking. The recipe calls for heating the ingredients to the soft-ball stage, or 234° F, then allowing it to cool undisturbed to approximately 110° F. If you stir during this cooling phase, you increase the likelihood that seed crystals will form too soon.
A seed crystal is a surface that sucrose molecules (that's the sugar) can begin to attach themselves toit could be a few sucrose molecules stuck together, a piece of dust, or even a little air bubble. Once a seed crystal forms, it grows bigger and bigger as the fudge cools. A lot of big crystals in fudge makes it grainy.
By letting the fudge cool without stirring, you avoid creating seed crystals. Stirring would help sucrose molecules "find" one another and start forming crystals. Stirring also introduces air, dust, and small dried bits from the walls of the saucepanall potential seeds for crystal formation.
When the fudge has cooled to about 110° F, you want to start the crystallization process. You start to stir, and keep stirring, until the candy becomes thick. The more you stir, the more crystal seeds you get. But instead of getting a few huge crystals (and grainy candy), you get lots and lots of tiny crystals, which make for thick, smooth candy.
There are two other candies that deliberately employ sugar crystals. One is fondant, a wetter version of fudge that you find inside soft-center chocolates. The other is rock candy, for which a sugar solution is left for days to form enormous crystals.
Fudge is one of the rare exceptions to the rule that sugar crystals are not desirable in candy. Tiny microcrystals in fudge are what give it its firm texture. The crystals are small enough, however, that they don't feel grainy on your tongue, but smooth.
When making fudge, heat and acid work together to convert sucrose – basic white sugar – into its two components, glucose and fructose. When these sugars are present, they prevent sucrose from turning into big sugar crystals.
Although fudge often contains chocolate, fudge is not the same as chocolate. Chocolate is a mix of cocoa solids, cocoa butter and sometimes sugar and other flavorings and is hard and brittle. Fudge is a mixture of sugar, dairy and flavorings that is cooked and cooled to form a smooth, semi-soft confection.
Heating the sugar and milk mixture allows the milk to dissolve more and more sugar, and by the time the mixture is boiling, all the sugar is dissolved. The general principle is that at a particular temperature, a given solvent (in this case, milk) can dissolve only so much of a particular solute (sugar).
If the sugar crystals are not properly dissolved before cooling, they can create a gritty texture. To avoid this, ensure that you stir the fudge mixture consistently and remove any sugar crystals that form on the sides of the pan using a wet pastry brush.
Fudge is one of the rare exceptions to the rule that sugar crystals are not desirable in candy. Tiny microcrystals in fudge are what give it its firm texture. The crystals are small enough, however, that they don't feel grainy on your tongue, but smooth.
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Fudge is one of the rare exceptions to the rule that sugar crystals are not desirable in candy. Tiny microcrystals in fudge are what give it its firm texture. The crystals are small enough, however, that they dont feel grainy on your tongue, but smooth. 
A seed crystal is a surface that sucrose molecules (that's the sugar) can begin to attach themselves toit could be a few sucrose molecules stuck together, a piece of dust, or even a little air bubble. Once a seed crystal forms, it grows bigger and bigger as the fudge cools. A lot of big crystals in fudge makes it grainy. 