Control the Environment

Just like chocolate, even properly tempered ganache will form unstable crystals if it is crystallized at too low a temperature. (See Polymorphism of Cocoa Butter diagram.) Properly made and handled ganache will set perfectly at 20°C/68°F. Further, ganache should not be refrigerated. Any attempt to rush the setting process by this method will be detrimental to the result. Refrigerating ganache creates centers that are too soft to handle when they return to room temperature, and, as with chocolate, the unstable crystals the ganache contains will transform to higher forms during storage, resulting in large, grainy-feeling fat crystals. (See Refrigeration of Ganache.)