Removing stains from granite countertops can be done with a poultice, also called a cataplasm. A poultice consists of an absorbent material and a chemical to remove the stain. There are different types of stains and each has a unique chemical for the poultice. For granite stains such as coffee, tea, mustard, soft drink, etc, the chemical used is 30-40% (by volume ) hydrogen peroxide.
For inorganic stains such as dyes, inks, etc, also use hydrogen peroxide except for ink, use rubbing alcohol.
For oil stains use pure acetone.
For biological stains such as mildew, mold, etc, use bleach or MB-9.
For metal stains such as rust, use Iron-Out.
There are 5 steps to removing a stain. keep in mind all granite is different so you may want to test on a small area of the granite to ensure there are no adverse effects.
Step 1. Mix poultice until you have a thick, putty-like paste (Ex. talc powder and hydrogen peroxide).
Step 2. Apply the poultice to the stained area, keeping it only on the stain, It should be around 1/4 of an inch thick.
Step 3. Cover poultice with plastic wrap and tape the edges down, let it sit for 24 hours.
Step 4. Remove plastic wrap and let poultice dry completely.
Step 5. When the poultice is dry, scrape away the paste and clean the counter top. If the stain remains, repeat the steps above until stain disappears completely.