Why is my blueberry jam 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.

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.

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.

I've made grape, blackberry, elderberry, pear and apple jams and jellies, as well as combinations of those fruits, for years with Sure Jell dry pectin. I sometimes stir in spices like cinnamon for grapes and blackberries, nutmeg for pears and apples, and even lavender flowers or mint. Elderberries grow wild in our area. I use the instruction sheet in the box. Occasionally, some of the jam or jelly turned out to have a gritty or grainy texture. This has happened more in the last couple of years.

As noted, it would seem to be important to use fresh pectin (watch the expiration date on the box), stir it very thoroughly into cold or room temp. juice before cooking, and, yes, be sure sugar is all dissolved by turning down heat and stirring a lot before boiling juice. I'm going to watch this more carefully.

Also, if possible, pick your fruit the same day you make the product, especially grapes. If you cook down grapes and let the juice sit in the fridge overnight before you make the jelly or jam, it will form gritty oxalic crystals that will definitely make your jam or jelly crunchy.

If you're making a product with apples or elderberries, know that they are naturally rich in pectin and will jell quicker and with less Sure Jell.

Good luck! I sell my jams and jellies at the fall church festival and make money for the church.