All good suggestions listed above. I have cleaned so many cork handles on my customers rods that I cannot remember. I mostly use Colgate diswashing liquid on a soft sponge with warm water and the cork usually comes up looking like new again. Occasionally I will also use an old toothbrush for scrubbing additional hard to clean areas. The baking soda works wonders as well, but I have a huge supply of dishwashing liquid to use up first. Only once did I receive a rod for reconditioning where the handle had never been cleaned and the poor thing was so caked with egg yoke from salmon roe that I had to bring out my secret weapon.........I used an industrial Scotchbrite srubbing pad to lightly scrub the handle clean. Even I had my doubts if I could ever get the handle clean at first, but after some very light scubbing the end result was amazing. My customer was shocked when he got his rod back!...... Ha! I would recommend that cork handles be cleaned at least annually to keep them looking good and lasting longer.
David Parker
Guild Certified Professional Rod Builder