Try oxygen bleach products. This is another name for sodium percarbonate, which is a compound made of hydrogen peroxide and soda crystals. Brand-name products include Clorox, OxiClean, Oxi Magic, and Bio Kleen. Mix the product with water as per the manufacturer’s instructions. Apply to the affected area and let it sit for up to an hour before scrubbing and rinsing.
Be sure to use these products in a well-ventilated area, and avoid contact with your skin. Always wear gloves to use these products. Always spot test commercial products in a small area on your grout to make sure the product won’t discolor, erode, or damage your grout. Don’t use any sort of bleach product on colored grout.
Use a commercial grout cleaner and whitener. There are many cleaners out there that are designed specifically for grout, and most of them can be purchased at hardware stores. Be sure to always follow the manufacturer’s instructions for use, and follow all the safety precautions.
Beware of chemical combinations. In case you find one chemical hasn’t worked and you want to try another, be sure to wash the area and wait a couple days before trying something new. Just like hydrogen peroxide and vinegar can combine to form peracetic acid, so too can commercial cleansers mix to form poisonous gasses, caustic liquids, and noxious fumes.
Stain the grout as a last resort. For dirt and stains that just won’t come clean from your grout, there are colorants you can apply to cover the stains and make your grout look like new. The area should be nice and clean, but if not give it a once over with your favorite cleaner and let the area dry overnight.
Pour a small amount of grout colorant into a container. Dip a clean toothbrush or grout brush into the color and apply it to the grout using even, back and forth strokes. Remove the excess with a paper towel, and allow to dry as per the manufacturer’s instructions.