Have you ever had honey that became solid and chunky over time? This state is know as crystallized or granulated hone. This natural phenomenon happens when glucose, one of the main sugars in honey, spontaneously precipitates out of the supersaturated honey solution. Honey crystallizes because it is a super saturated solution. This super saturated state occurs because there is so much sugar in honey (more than 70%) relative to the water content (often less than 20%). Glucose tends to precipitate out of solution and the solution changes to the more stable saturated state.
At room temperature, crystallization begins within weeks or months. The crystallization process can be avoided with proper storage, with an emphasis on proper storage temperature. For long-term storage, the use of air-tight, moisture-resistant stainless steel drums are recommended. Cool temperatures (below 50 degrees Fahrenheit) are ideal for preventing crystallization. Moderate temperatures (50=70 degrees Fahrenheit) generally encourage crystallization. Warm temperatures (70-81 degrees Fahrenheit) discourage crystallization but degrade honey. Very warm temperatures (over 81 degrees Fahrenheit) prevent crystallization but encourage spoilage by fermentation as well as degrading the honey.
SOURCE: National Honey Board, Honey: A Reference Guide to Nature’s Sweetener.