You wouldn't know it from looking at them, but granite countertops--like all natural stone surfaces--are porous. They can absorb stains, grease and even odor.
It's important to keep your granite clean, especially after preparing food on the countertop. It's also important not to use harsh chemicals that can damage the finish.
Acids are a no-no (don't let anyone advise you to use vinegar). There are specially formulated granite cleansers available, but it's just as easy--and less expensive--to make your own.
Mix the Solution
You should never use abrasive cleansers on granite, as the glass-like finish can be scratched up as surely as if you'd used it on a window. It's also important not to let water sit on it for extended periods of time, as it can become a pathway for stains to get into the surface.
The best solution is a mild, pH-neutral soap to clean, combined with rubbing alcohol to promote quick evaporation of the liquid. Put about 1/4 cup of rubbing alcohol in a quart-sized spray bottle.
Add three or four drops of dish washing liquid. Fill the rest of the bottle with warm water, filling it slowly to avoid creating a lot of suds.
Spray the Solution
Apply your alcohol-dishsoap homemade cleaner generously to one section of the countertop, coating it with the spray bottle. Let it sit on the surface for a minute (no longer).
Then use a soft cloth to work the solution around the surface in that one section. Buff it gently in a circular motion.
Buff until it's dry, then move on to the next section. Granite can pick up colors and stain, so it's a good idea to use only white cloths for light-colored countertops, as dark or dyed cloth can transfer that color into the surface.
Keep your cleaning solution under the sink and use it daily, right after using the countertop for food preparation or right before you go to bed. Avoid cutting food directly on the countertop, as even a small scratch on the surface can collect germs and dirt.
Wipe up spills as soon as they happen. In addition, you should re-seal the countertop about once a year to help prevent stains and grease from working into the surface.
Granite sealant is applied similarly to your cleanser, except you need to let it sit on the countertop for about five minutes after spraying it, so it can seep into the surface, then wipe and buff as before.