If you drink tea often, you may have noticed that as soon as you add a drop of lemon juice to it, the color changes. No, it's not black magic or witchcraft: it's chemistry. It's certainly happened to you with black tea (for obvious color reasons), but it also happens with other types, even lighter ones. Tea contains molecules called polyphenols, specifically thearubigins, which are sensitive to pH, or how acidic or basic a solution is. Lemon juice is acidic (thanks to citric acid), and when you add it, it lowers the pH of the tea. The pH of tea without lemon is usually around 6-7, while with the addition of lemon juice, it easily lowers to around 4-5, depending on the amount of lemon.
This change in pH causes thearubigin molecules to "protonate" —a chemical process in which a molecule or atom acquires a hydrogen ion— which alters their three-dimensional structure and electron distribution. This causes the molecules to reflect light differently, making the tea appear less intense, or "lighter." It may seem like a snap of the fingers, but there's a truly fascinating "molecular dance" behind it, one that deserves to be explained.
Why Does Tea Become Clearer if We Add a Few Drops of Lemon?
Now that the initial premise is out of the way, let's delve into the tea to fully understand this chemical phenomenon. When we brew tea, we steep leaves from which many substances are extracted. Among these are polyphenols—and thearubigin is precisely one—responsible for that amber-brown/reddish color we know so well. These molecules have a certain "molecular structure" that determines how they absorb and reflect light.
If the environment remains neutral or slightly basic, they retain their darker color. But if the environment becomes acidic (i.e., the pH decreases), the molecules change shape slightly: protons (H⁺ ions) bind or reconfigure, influencing how electrons "move" around the molecule.
A chemical explanation that can actually be summarized much more simply: The more acidic the liquid becomes (i.e., the more "hydrogen ions" there are), the more the tea molecules slightly change shape and begin to reflect light differently, making the color appear lighter or, more precisely, less intense.
Is Tea Better With or Without Lemon?
Now let's (finally) put chemistry aside for a moment and focus on the true taste of tea. The question, after all the scientific explanation, arises spontaneously: lemon or no lemon? The answer for true tea lovers, even those who call themselves purists, should be obvious. The beverage should be enjoyed pure and not compromised with lemon, sugar, or sweeteners. Adding other flavors could alter the harmony of the flavor and cover the delicate notes.
There's also the other side of the coin, however, and it's worth considering that, from a health perspective, a few drops of lemon can be beneficial. Lemon juice provides vitamin C, which is very beneficial for your health. If you want the best of both worlds, you can opt for a very moderate amount of lemon, so as not to overwhelm the flavor but still get that nutritional boost. Alternatively, use lemon only when making more robust teas (black, for example), which are less delicate, where the natural flavor profile better resists the added acidity.
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