Most pure honey will, in time, go solid or semi-solid. This is known as granulated or crystallised honey. It has not gone bad! The wonderful thing about good quality honey is that it never spoils – honey over 2000 years old, removed from the Egyptian Pyramids was still edible!

Granulation is natural. It happens when glucose, one of three main sugars in honey, precipitates out of the supersaturated honey solution. The glucose loses water and takes the form of crystals.

Several things influence granulation:

1) The glucose content and moisture level; Honeys with a moisture content of less than 17% are more likely to granulate than those with content closer to 20%.
2) Floral source of honey. Ivy honey & Oil Seed Rape granulates rapidly (a few weeks), heather honey never. The overall composition of honey, which includes sugars other than glucose and more than 180 identified substances such as minerals, acids and proteins, influences crystallization.
3) Temperature. Honey granulates most rapidly around 8°C and temperature changes accelerate the process.

To return granulated honey to a liquid state:

The secret is to use a little heat, enough to re-liquefy it without overheating . Avoid overheating as heat can adversely affect the flavour of honey and may kill some of the valuable enzymes in the honey.

There are two ways to do this:
1) Microwave – open the container and use short bursts (30 seconds), wait 20 seconds between bursts, this will keep it from overheating and give you a chance to see the affect. Once honey starts warming up closing the container and shaking will help to dissolve the crystals.
2) Warm water – open the container and place in a water bath  (as warm as you can keep a finger in it). Let it stand for about an hour, stirring occasionally. Repeat if needed.