I have a favorite mug, plain white ceramic with a chipped handle that I refuse to throw away. After a year of daily coffee, the inside looked like someone had painted it brown. Dish soap alone never touched it.

Those stains are tannins from the coffee, and they bond to the porous surface of the mug. The good news is they come off with things you already own.

Baking soda and a little water

Sprinkle baking soda in the mug, add a few drops of water to make a paste, and scrub with a sponge or your fingers. The paste is mildly abrasive, so it lifts the stain without scratching the glaze. This is the method I use on the stubborn ring at the bottom, and it works in about a minute.

Salt and lemon juice

Cut a lemon in half, dip the cut side in salt, and rub it around the inside of the mug. The acid breaks down the tannins and the salt scrubs them off. Rinse and repeat if needed. It leaves the mug smelling like citrus instead of old coffee, which is a nice bonus.

White vinegar soak

For really stained mugs, fill them with white vinegar and hot water, about half and half, and let them sit for an hour. The vinegar loosens everything, and a quick scrub after the soak does the rest. Do not use this on mugs with gold trim, because vinegar can eat through the metallic finish.

Toothpaste in a pinch

Plain white toothpaste, not gel, works as a gentle scrubber too. Dab a little on a damp cloth and rub the stain in circles. It is a weird trick but it genuinely works, and it is handy if you are out of baking soda.

Stop the stain from coming back

The real fix is rinsing your mug right after you finish. Coffee dries into the pores and that is when it becomes a stain. Thirty seconds of hot water after your last sip keeps the mug white for months. I still forget sometimes, but now I know the baking soda paste rescues me in a minute.