It seems like every time I need brown sugar, the package in my pantry has completely dried out and become a rock-like mass. Frustrated by this constant problem, I decided to try several methods of keeping brown sugar moist to see if one is better than the rest.
My mom always put a slice of apple in with her brown sugar, but it would eventually shrivel up. I tried keeping a piece of bread in my sugar, but it got moldy. Next I tried a damp paper towel on top of the sugar, but that caused it to become soggy in some spots and crystallized in others.
Call me a slow learner, but I finally found the solution. Now I leave the sugar in its original bag and close the top loosely with tape, a rubber band, or a clip. Then I put it in a zip-top plastic bag and tuck in a damp paper towel. This way, the paper towel doesn’t touch the sugar and make it soggy, but it keeps the air around the bag of sugar humid enough that there’s no rock formation going on. I just change the towel every once in a while, and my brown sugar stays soft and moist for months.