Brown sugar is mostly sucrose (85-92%) and contains varying amount of caramel, molasses selected for color and taste. The more molasses, the stickier the crystals, the darker the color and the stronger the flavor.
It contains small amount of acid, and thus can be used with baking soda to provide some leavening. Brown sugar has to be stored in airtight container to prevent hardening and lump formation. It is more frequently used in baked goods as dry mixes, meat glazes, sauces and condiments.