While brown sugar is usually the clumping culprit, causing frustration for many cooks and bakers, white sugar can also fall prey to this problem, especially in moisture-filled climates. When excess humidity and moisture gets into white sugar that is improperly stored, the sugar will liquefy, which can cause it to group together in large clumps. If you discover that your white sugar contains clumps, you can use a variety of methods to rid the sugar of those annoying clumps and return it to its original texture for use in everyday items, from beverages to recipes.
Pour the lumpy sugar into a blender or food processor. Blend or process on a low speed until the clumps have broken up and the sugar is smooth throughout.
Place the sugar in a heavy-duty freezer bag with a zip-top seal, ensuring that it is completely sealed. Break up the clumps by gently pounding them with a hammer or the flat side of a meat tenderizer mallet.
Put the sugar clumps in the receptacle of a spice grinder and grind them until the clumps are broken up.
Break up smaller sugar clumps with a mortar and pestle.
Prevent sugar from clumping in the future by pouring it in to a plastic bag with a zip-top seal, pressing out as much of the air as possible and sealing it for storage. You can also store white sugar in an airtight container.
When stored in an airtight bag or container, white sugar will keep indefinitely.