The enamel on your teeth is the hardest substance in the human body, but it is not flat and smooth. Actually, your tooth enamel contains microscopic pits and ridges that can hold particles of food and drink.
Coffee contains natural compounds called tannins that cause pigments to stick to your teeth. Pigments from dark-coloured drinks, such as coffee, tea, and soda, can become embedded in the cracks and ridges of your enamel. Over time, this leads to permanent discolouration of your teeth.