In a spray bottle, mix 4 tablespoons of baking soda with 10 centimeters of white vinegar. The mixture will start to foam like a mini-volcano: don’t worry, this chemical reaction is completely normal.
Spray the baking soda-white vinegar mixture on the dirty tile joints, then leave the product on for 24 hours until it can act.
Scrub your joints using a toothbrush or sponge, rinse with water, and admire the result!
Good to know: to prevent fairly exposed tile joints (in your kitchen or bathroom for example) from getting dirty too quickly, you can cover them with a varnish for tile joints which will protect them from stains and humidity.