My bathroom grout went from white to a color I can only describe as regret. I tried sprays. I tried scrubbing with a brush until my arm hurt. Nothing touched it. Then my mom watched me suffer for about five minutes and said, very calmly, that I was overpaying for fancy cleaners when I already owned the good stuff.

The thirty-second paste

Mix baking soda with a little water until it forms a thick paste, about the consistency of toothpaste. That is it. No waiting, no measuring, no special order. If the grout is really dark or greasy, swap half the water for white vinegar. Just do not use vinegar on natural stone tile, it can etch it.

How I actually got the grout clean

Here is what worked after years of doing it wrong:

1. Spread the paste over the grout lines with an old toothbrush or your finger.
2. Let it sit for ten minutes. Do not scrub yet. Let it work.
3. Scrub along the lines with a stiff brush, not in circles.
4. Rinse with water and wipe dry with a cloth.

Why this beats the spray bottles

The sprays you buy are mostly water with a little bleach and fragrance. The paste actually sticks to the grout instead of running down the tile and draining away, so the baking soda gets time to break down the film that is making the grout look gray.

When it will not come clean

If your grout is still stained after two passes, it may be beyond cleaning. Old, porous grout soaks stains in like a sponge. In that case, I seal the grout after cleaning it so the next spill sits on top instead of sinking in. A cheap grout sealer from the hardware store has kept my bathroom looking decent for months now.