The best grout cleaner is Zep grout cleaner and brightener as well as Scrub Daddy and Black Diamond Cleaner.
Other good grout cleaners are Soft Scrub Cleanser with Bleach, Goo Gone Grout and Tile Cleaner, Star Drops The Pink Stuff, CLR Brilliant Bath, Hour Bathroom Cleaner, Oxo Good Grips Grout Brush, Remover Tilex Mold & Mildew, Apply A Grout Sealer, Better Life Cleaner TUb & Tile, Scrubbing Bubbles Bathroom cleaner and Clorox.
You can also use vinegar or even hydrogen peroxide and even baking soda to clean grout.
To whiten your grout using some baking soda and bleach or hydrogen peroxide, create a paste of some baking soda and either some hydrogen peroxide or bleach.
Then apply the baking soda paste to the grout and allow it to sit on the grout for a few minutes.
Then scrub and rinse the grout.
If the grout stain or grime is more stubborn you can use a commercial grout cleaner or use steam cleaning of the grout.
Professional grout cleaners often clean the grout using a combination of specialized cleaning solutions and equipment to effectively remove any dirt and stains.
Professional grout cleaners commonly use low pressure, hot steam cleaners to loosen and expel any dirt particles within the grout and they sometimes also use pH balanced cleaning solutions such as hydrogen peroxide and baking soda mixtures or even purified water, ionized water or alkalinized water.
Low pressure hot steam cleaners are machines that use steam to penetrate the grout and loosen the dirt and grime from the grout for easier removal.