Granite can be discolored by acids and other harsh cleaners, so when it comes to cleaning, always start conservatively. Avoid abrasive cleaning pads, which can dull your cornhole boards polish, and opt instead for soft cloths and softer bristled brushes. Microfiber products work especially well.
Cleaning items to always Avoid!
Acidic cleaners, anything with citrus or vinegar.
Ammonia based cleaners, including products like Windex.
Bleach cleaners, including Clorox wipes and similar products.
Start by wiping off the surface with a soft cloth, clearing any dust, pollen or debris.
Mix a few drops of a neutral cleaner, stone soap or a mild liquid dish detergent with warm water.
Wipe down with a soft cloth, soft bristled brush or sponge.
Rinse thoroughly with clean water again to avoid buildup of soap residue.
Dry with a clean soft microfiber cloth.
Generally this will be the only cleaning method you will need. Timely cleaning up of spills is important to prevent staining.
Stain removal suggestions:
If a light stain is noticed, and basic cleaning has not provided desired results and you need a little more power.
Make a 50/50 solution of isopropyl alcohol and water. Spray the solution onto the area of concern, leave up to 5 minutes, and then rinse with a soft cloth.
For bad stains, make a baking soda paste.
Take a bit of baking soda and mix with water or a little hydrogen peroxide, place on the stain, and leave overnight, or up to 24hrs if needed. Wipe the paste away with a damp cloth.