Why is my blueberry jam grainy?

Question

I recently made and canned blueberry jam for the first time, using this recipe and canning instructions.

I filled all my jars & 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?

Answer 1

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.

Answer 2

There are many causes for the jam being grainy, but most commonly, as @hobodave suggested, is due to inadequate dissolution of sugar.

The test is simple. Get some jam into a bowl, add a little bit of water, stir, does it resolve the problem? If yes, then it is a dissolution problem. There, you may want to change the method of making that jam -- if your blueberry, is, for example, containing more sugar than the recipe-maker's blueberry had... or if the measuring cup is broken (j/k).

If you can tolerate the current batch, I think there is little to do to 'save' it by adding water/reheating as these destroy flavors.

Answer 3

Graininess caused by excess undissolved sugar is fairly obvious. The grains will be sweet and will dissolve on the tongue.

Alternatively, with some fruit including blueberries, the skins of the fruit can be dry or tough and stay in grainy fragments in the jam. Again, this is obvious. The individual shreds will be dark and flat, etc.

Another, in my opinion, more subtle and more likely is that the graininess was caused by excess pectin gelling.

When pectins overgel they pull tight and form small, stiff granules. These are bland and rubbery. Very unlike sugar or fruit particles.

Normal, thermally reversible, pectin does not often over gel. If it does, reheating and possibly adding a little liquid will fix the problem.

LM pectins, on the other hand, can over gel fairly easily and as they are not thermally reversible it is impossible to fix the jam when it happens. See this article about pectin, in particular the 5th page about LM pectins.

Blueberries are very high in natural pectin. Blueberry puree will sometimes set up as jam without any added sugar or pectin. This abundance of pectin may have caused the added pectin to over gel and form the graininess that you saw- especially if you were using low sugar pectin in your jam recipe.