The clumping of brown sugar is the result of the molasses coating drying... There are terracotta pieces sold to reduce or prevent the drying effect. They are soaked in water, wiped dry and placed in the container to help retain moisture.. Being a cheap sort and
one that would rather make rather than buy , I ended up making my own terracotta moisture maintainer..I purchased a new flower pot, soaked in water for a couple of hours then cut it into pieces starting with the rim. To do this I used a thin masonry disc on my
4 1/2" angle grinder. It worked amazingly well, with the only drawback being dust. All corners and edges of the pieces were rounded too finish things off. Some of the pieces are small enough to fit in my smaller shaker jars .. All this for $2.00 and some time.