Reprinted with permission of McGill University's Office for Science and Society. The original article by Ada McVean B.Sc. can be found here.
Do you ever try to wash a mug only to be confronted by tea stains that just won’t budge? A little bit of chemistry may be just what you need to get your mugs back to white.
Brewed tea, green or black, contains many compounds, including many polyphenols. These are compounds found naturally in tea leaves that have antioxidant properties and contribute to the taste of tea. However, they are also responsible for the stains left in your mugs and teapots.
Polyphenols are a large group of complex molecules that are structurally similar in that they all contain simpler components known as phenols. Tannins are a class of polyphenols that provide tea with its characteristic hue, and are responsible for those annoying stains. Being largely impervious to scrubbing, how can these stains be removed?
A little bit of chemistry.
Black tea has a pH of 4.9, meaning that it is slightly acidic. While tannins encompass a wide variety of compounds, they all tend to be slightly acidic. As such, to remove them from the sides of your mug, you need to neutralize them with a base. the most readily available of which tends to be baking soda.
Just make a paste of baking soda and water, rub it onto your stained crockery, leave it for 20 minutes or so, and then wipe it off with a sponge. It certainly worked wonders on my now much-cleaner teapot.