Here's the problem: properly extracted and stored honey will never go bad (they've found edible honey in millenia-old Egyptian tombs), but it does crystallize, because the sugars are supersaturated in the water, so the little flecks of pollen and other natural goodness in the honey causes it to precipitate. Again, it doesn't make it go bad, but it does make it hard to use, as you have to scoop it rather than drizzle it.
So what to do? Heating it will reliquify it, but you need to be careful, as part of the magic of raw honey is in the enzymes and proteins that will break down if it's heated too much (I haven't found any solid numbers, but 120° F seems to be a reasonable upper limit). Also, as you get into higher temperatures, you carmelize the sugars and change the flavor.
Thus, my usual strategy has been to take my jars of crystallized honey and give them a slow, warm bath on the stove. Effective, but not efficient: to ensure that I don't accidentally pasteurize or carmelize the honey, it can take 4 or 5 hours on low heat, and with only one small stove top, that can mean days to get through dozens of jars.
But wait! I've got a hot tub in my back yard. And it's set to 104° F! Let's see how it worked:
Brilliant, just brilliant!
PS Why doesn't store-bought honey crystallize as quickly? Likely higher moisture content (i.e., it's been diluted with water).
