Tannins add a pleasant bitterness to popular beverages, such as wine and coffee, but they are notorious for leaving difficult stains. Brown stains on teaspoons and mugs are a nuisance to tea and coffee lovers, because these stains are seemingly impossible to remove if you attack them with regular dish detergent. The teaspoon tannin stains will gradually worsen if you repeatedly use the spoons in tea or coffee, so remove tannin stains from flatware, as needed, with common kitchen ingredients.
Soak the stained spoons in a mixture of one part warm water to one part white distilled vinegar for 10 minutes. Do not soak the flatware for a longer period or overnight, as this can damage stainless steel.
Remove the spoons from the mixture, and discard the liquid.
Coat remaining stains with baking soda, and scrub it in small, circular motions with a damp sponge.
Rinse the spoons with clean water, and dry them with your usual method.
Use this process with tannin-stained mugs, too.