Like any plant, the tea plant is composed of hundreds of different compounds. Some of the most interesting ones fall into the category of polyphenols, so called because of their molecular structure. These compounds, specifically a sub-category called “tannins” are responsible for the dark color you sometimes get in tea and they also account for the possible health benefits of tea.

The tannins themselves are light colored but when they react with iron they form dark colored complexes. Indeed, historically inks were made by extracting tannins from oak trees and combining them with iron compounds. But where does the iron come from when making tea? The water! Now, we are not talking about chunks of metal floating around, we are talking about iron compounds dissolved in the water. This happens as water flows through the ground which contains a variety of iron compounds. In different regions, tea will be different colors, depending on the iron content of the water.

Some water filter manufacturers advertise the fact that water made with the filtered water will be lighter in color. This may be true but is of no real consequence. The filter removes iron from the water so the complex with the polyphenols cannot form. And how about the lemon juice connection? It turns out that the iron-polyphenol complex is not stable in acids and lemon juice contains citric acid. So that is why the tea gets lighter when it is added.