As the bees travel from flower to tree and back again to collect sap and pollen they remove a lot of water from the nectar. The resulting honey is primarily a solution of natural sugars and water that remains in a state of flux, always in the process of either further drying out in the direction of a dried crystallized solution, or further liquefying, pulling water molecules from its surroundings, and gently liquefying.
The process of crystallization of honey occurs when glucose, one of the natural sugars present in raw honey, spontaneously precipitates out of the supersaturated honey solution. The glucose slightly dries in the air, giving up water molecules and becoming crystalline glucose. These crystals create a lattice form which generates the semi-solid state of the “crystallized honey”. The crystallization generally occurs slowly, over the course of weeks or months. During this process, the higher moisture content liquid honey remains the top of the jar, while the heavier crystalline structure develops on the bottom of the jar.
In general, honeys will crystallize quicker in cooler environments, and resist crystallization in warmer surroundings. The rate at which raw honeys crystallize is a function of the variety of the honey, and the various sugars in their differing proportions, depending on the flower source for the honey. Some honeys, such as Tupelo and Black Button Sage, are known to resist crystallization completely, and some Acacia honeys remain liquid for years. Other honeys such as clover crystallize more rapidly in normal conditions.
Storing honey in the fridge, then microwaving it is the worst thing to do. If you observe crystallization, loosen the lid and place the jar in a pan of warm, but not boiling, water. NOTE ABOUT MICROWAVING HONEY: this high heat will kill the valuable enzymes, anti-oxidants, and complex carbohydrates that nature has provided, leaving behind little more than a glucose-rich sweetener. Store honey in a dark corner of the cupboard and it will last for years.