Why is my blueberry jam grainy? I recently made and canned blueberry jam for the first time, using this recipe and canning instructions. 

I filled all my jars &amp; canned them, but there was a little jam left in the pot. It was a bit grainy, but I thought it was just from being the last bit in the pot. 

I just opened one of the jars, though, and the jam inside is grainy as well. 

Does anyone have any idea what I might have done wrong?

EDIT: I don't think it's the sugar. Could something about the pectic make it grainy?
Were your blueberries grainy? I occasionally get a pint that have a grainy texture. I've heard that this means they aren't quite fresh, but they usually taste just fine despite the texture. I'm not sure if this particular graininess translates to a jam though.

Jam can also get grainy from sugar that isn't fully dissolved. This can happen more easily with larger batches, since the fruit can start to boil before the sugar is fully dissolved.

For your particular recipe, perhaps a more thorough stirring after adding the sugar would help. You should be able to turn the heat down once you add the sugar so that you can stir it thoroughly before going back to high heat to boil for that 1 minute.