There is only one good way to CLEAN grout. If you want to zap, erode,
bleach, stain or contaminate grout. Check the other postings.
By using superheated dry vapor steam (far exceeding 190 degrees) you
can apply this chemical-free treatment through a hose and small brush
while standing. The heat and light agitation emusifies grease, dirt
and grime so it can be wiped with a towel. There may be some
applications where this won't work real well (rust, calcium, acrylic
sealed), but generally you'll restore grout to the original color. You
may use citrus based degreasing solvents to pretreat kitchen areas. I
can tell exactly where other "solutions" have been tried and failed
because the grout was deteriorated or discolored. Then you have saw or
grind out the old stuff and (hopefully) match with new. Regardless of
the claims, most chemical agents will ruin your grout because they're
acidic, or corrosive and decompose the integrity and/or color of
I have information on the best dry vapor systems for home and
commercial use if anyone is interested.