Steam is the best, but not always available to use.
Other then that a good stiff brush with scrubbing bubbles, or strong detergent cleaner will do the trick. You will get a lot of great responses also on this subject if you do a search at the top of the page under cleaning grout. Regardless of what method you end up trying, be sure to re-seal the tile and grout once done so the next cleaning will be easier and faster.
I have tried this and though it can be a bit time consuming, very effective.....
**Stained grout or grout with mold and mildew can be cleaned with bleach or vinegar. Mix one cup of bleach or vinegar and one cup of water in an empty spray bottle. Shake well before each use and spray directly on stained grout. Let the cleanser sit for 15 minutes, scrub grout with a soft-bristle toothbrush and rinse it clean with water. Do not use bleach on colored grout.
Read more: Ceramic Tile & Grout Cleaning Tips | eHow.com http://www.ehow.com/list_6696114_ceramic-tile-grout-cleaning-tips.html#ixzz2MaFv2oet
Zap Grout Cleaner is the best I have found (note-NOT Zep). I 1st purchased it at Home Depot but it is now only available online. It costs around $10 a bottle and is available for white or colored grout. They sell small sponges to go with it which is helpful not to tear up your cloths and not leave threads on rough texture. The second you squirt it on you will see the difference. Amazing find!
Sweet! I'm getting ready to have our annual Spring Yard Bash and my floors are so ready for a face lift! Thank you Terry! I shall order today!
Be sure to check if its muriatic acid or not. That chemical will brighten up white grout when it hits it as well. But it will damage the grout and perhaps the tile, depending upon what you have. My bet is that they tell you to wear gloves with the product and that you only put it on the grout which is why they give you the small sponge to direct it to the correct areas.
Just be careful with what ever chemical it is that they suggest and if it does contain a diluted form of muriatic acid that you keep the windows open and pets away while you do this cleaning.
Muratic acid is used a lot in stone cleaning.
As to the previous comment from Woodbridge, I need to order some again, so I can't comment on the ingredients. I have had no problems with Zap damaging grout or tile, or my skin, nor has the odor been too strong. But it is important to get the right kind, one is for white and the other for colored grout. I have only worked with the white because that's what I have. I also have only used it on floor tile, so I cannot comment on wall tile. I'm sure they will be able to give you answers on the site. All I can say is it has worked wonders for me.
Taken from the ingredients on the product label
You are advised never allow Zap to come in contact with any of the following substances: Wood, Paint, Vinyl, Enamel, Formica, Acrylic, Marble, Granite, Concrete, Aluminum, Corian, Plated Metals, Brick or Colored Porcelain or Grout.
The reason for this are the active ingredients in this restorer... Sulfuric Acid and Muratic Acid.
It is also available at Lowe's if your interested in purchasing this without going on line.
Vinegar and water with tooth brush is the best option. Easiest and cheapest. just wipe up after you scrub 😆 We tried peroxide and baking soda, it worked but clean up was crazy. Had to mop at least 10-12 times.
Use muriatic acid (diluted hydrochloric) found in swimming pool supplies. "Paint" on with an appropriate brush--ask someone which kind at the supply place-- and let sit , checking it by wiping away a section until it'seems like stains have been removed. It actually etched away the stained grout, so be cautious. Rinse with water. Consider sealing the grout with a clear epoxy sealant to keep the grout from getting bad again.