Why does tea change colour when a lemon is put into it?

The color change in tea when you add lemon is due to a chemical reaction between the flavonoids in the tea and the citric acid in the lemon.

Here's the breakdown:

* Flavonoids: These are natural pigments found in tea that give it its color. In black tea, the main flavonoid is theaflavin, which has a reddish-brown color.

* Citric Acid: This is the primary acid in lemons, responsible for their sour taste.

* The Reaction: When citric acid is added to tea, it interacts with the theaflavin. This interaction causes the theaflavin to change structure, resulting in a lighter color. The exact chemical reaction is complex and involves protonation and deprotonation of the theaflavin molecule.

Why the color change is different for different teas:

* Black Tea: The change in black tea is more noticeable because theaflavin is a stronger pigment. The color can turn lighter, more yellowish, or even have a slight greenish hue.

* Green Tea: The change in green tea is less dramatic because it contains less theaflavin and more catechins, which are less affected by citric acid. The color might become slightly lighter, but not as drastically as black tea.

In short: The lemon doesn't directly change the color of the tea. It reacts with the flavonoids present, causing them to change their structure and thus alter the color.