Controlling Crystal Size and Candy Texture

The cook has to worry about premature crystallization because candy texture is affected by the syrup temperature at which crystallization begins. Generally, hot syrups produce coarse crystals, and cool syrups produce fine crystals. Here’s the logic. Because more sugar molecules will arrive at the crystal surface during a given time in a hot syrup with fast-moving molecules than in a cold, lethargic one, crystals grow more rapidly in hot syrups. At the same time, because stable crystal seeds are less likely to form at higher temperatures—an aggregate of a few sugar molecules is more easily knocked apart in fast-moving surroundings—the total number of crystals formed in a hot syrup will be lower. Put these two trends together, and we see that when a hot syrup begins to crystallize, it will produce fewer and larger crystals than a cool one, and therefore a coarse texture. This is why recipes for fudge or fondant, candies with a fine, creamy texture, call for the syrup to be cooled drastically—from 235°F/113°C down to around 110°F/43°C—before the cook initiates crystallization by stirring.