Cola stains are hard to remove because they are complex stains. Cola contains sugars and tannins and many colas have alcohols. The most efficient method of removing dried cola stains is to first attack the sugars and alcohol with glycerin and then work on the tannin. Glycerin can be purchased cheaply at a drug or craft store.
Removing A Tough Cola Stain
Use a soft sponge or cotton ball to apply the glycerin in a circular motion. Rubbing gently for a few minutes will lift out the sugars and alcohol from the stain.
Rinse with cold water to remove the glycerin. This will remove the sugars other non- tannin ingredients as well.
Mix 1 tsp. of pH neutral shampoo with 2/3 cup water and 1/3 cup white vinegar. This detergent mix will remove the tannin.
Use a soft white cloth. Dip a corner of the cloth into the detergent mixture and using gentle circular motion rub the stain. This step might need to be repeated several times to get out all of the tannin.
Wash in cold water with a gentle detergent of your choice. The stain should be completely gone.