During the holidays, I read that keeping brown sugar in glass jars help to keep them from getting concrete hard. I put the brown sugar in two jars (did not have a jar large enough for the entire box), and have been happily using the brown sugar. However, this morning, I ran out of sugar in the jar I already opened and had to open the second jar. Concrete hard! I don't know what happened. Is there a difference between jars? Is there anyway to soften the sugar in the second jar?