Storing Brown Sugar: To keep your brown sugar soft, be sure to close the enclosed plastic bag tightly after opening. Or keep it in a sealed zip-top plastic bag. Substitution: You can replace white sugar with brown sugar in recipes. (1 cup white sugar - 1 cup firmly packed brown sugar.) Expect a slight butterscotch flavor and a bit more moistness in whatever you're baking. Removing Lumps: To eliminate any lumps in brown sugar, simply pulse it a few times in a food processor. Softening: Soften hardened brown sugar overnight by putting it in a sealed container with a damp paper towel or a slice of apple.