Submitted by artgreenist t3_zkxlem in askscience
I know that adding lemon changing colour of tea, making it lighter. And taste of tea has less bitterness. But does it mean that lemon acid neutralises or break down tannins and caffeine (which responsible for bitterness)? Or they are still there?Especially caffeine
UPD I've read that acid reacts with polyphenol pigment, making tea colour lighter. But anyway, the answer about tannin and caffeine is open
Indemnity4 t1_j050jr4 wrote
No change.
Lemon juice does nothing for tannins or caffeine. It won't affect the amount extracted, it won't change the extraction time. No change.
Lemon juice is mostly water. That's obviously doing nothing other than slightly diluting your brew.
Next is sugar. Lemons really contain quite a lot of sugar, despite the sour taste. That's also doing nothing to change the chemistry of your brew.
Increased acidity? Also nothing. Tannins are already weak acid molecules. They aren't changing due to adding in another weak acid. Caffeine? Also not really affected by mild changes in pH.
Surprising change? Calcium and taste perception. Tea and coffee actually kind of taste really bad when made in ultra-pure water. Same goes with beer and soda too. That's why claims of such and such drink comes from the purest natural mountain stream etc are true, the water quality has an effect on taste perception. Everyone really does enjoy the taste of mineral water as well as artificial mineral water (tap water with minerals added). The optimum concentration of calcium for improved taste is somewhere around 100-200 mg/L. That's kind of a lot and would normally be considered "hard water" that forms scale to block your pipes, requiring cleaning.
What's unique about adding lemon (and citrus juices) is they contain citric acid. Citric acid just magically happens to love calcium, same way two magnets of opposite attraction stick to each other. By adding lemon juice to tea/coffee brew, you not only modify the overall taste by adding citrus oils and sugar, you also pull out some of the calcium goodness from the water. Overall: it makes the tea/coffee taste a little bit weaker, despite containing all the same quantities of food chemistry.