Why does honey crystallize?
All honeys will sooner or later crystallize. Crystallization is simply honey returning to its natural state. Solidifying depends mainly on what type of flowers the bees gathered the nectar from, and how it is stored. Honey is a combination of glucose and fructose, which are both forms of simple sugars. Honey has many antioxidants, proteins and minerals.
Some honeys have higher levels of fructose therefore take longer to crystallize.
If the bees gathered the pollen from flowers with sweeter nectar, then that type of honey will take longer to crystallize. If the nectar is slightly less sweet, the honey may solidify slightly quicker.
Some honeys are simply slower to crystallize whereas others solidify faster. The way to help maintain honey liquid, is to keep it at the right temperature.
The best storage temperature for honey is 64-75° Fahrenheit (18-24° Celsius) Storing it in an airtight container away from strong light and dry place is best. Do not store in the refrigerator as this will only speed up the process of crystallization.
For practical purposes usually a shelf life of one to two years is stated. Honey that is properly processed, packaged and stored retains it quality for a long time.
Gentle heating can easily reverse crystallization of honey. This is done by boiling a pot of water, remove the pot from the heat, place the jar of honey in the hot water until it returns to it is liquid state.
Sources; National Honey Board USA http://www.honey.com/images/downloads/crystallization.pdf