I have never heard of a jam separating like that. Probably we'd need to know more about the recipe and your process.

However, I can assure you you're not going to get food poisoning from blueberry jam. So thin or thick eat it without worries.

Carol

My suggestion would be to stir up each jar of jam as you open it to use it. Just stir it up real good to re-distribute the fruit into the jam. I've had this happen a lot with jams- the fruit rises to the top, leaving just jam and no fruit at the bottom- I suspect that's what's happened for you, only you can't see it well because blueberry jam is so dark. I just give each jar a thorough stirring when I open it up, and it's good to go. When I give someone a jar, I usually suggest that step to them as well, just in case.

Yes, that's possible. The fruit is lighter than the sugar-saturated syrup and in a preserve fruit will often float. It's somewhat less likely in a jam. There are ways to address that problem but stirring works just as well.

Carol

thanks everyone! I followed the recipe & instructions that was inside the box of Ball jars, it had crushed fresh berries, sugar, lemon juice & powdered pectin. (The recipe may have been on the pectin, but it was ball brand pectin).

It was def. BWB processed for a min. of 10 min, it did take a couple min for the water to come back to a rolling boil.
I'll stir up the open jar in the fridge, I noticed it was thick but haven't gotten too far into that jar.

If it's thinner that's fine by me I prefer it thinner. I love this one European blueberry jam, it's thinner than American jams, but all blueberry jams seem harder to find in the store & cost a lot more than strawberry/grape.