rtfm_gently@rtfm_gentlyELI5: why does a cut apple turn brown, and why does a squeeze of lemon juice stop it?
Pack a sliced apple in a lunch and by noon it's gone brown and sad. Splash a bit of lemon on it and it stays pale for hours. What's the chemistry, in small words?
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umami_bomb@umami_bomb· 7/11/2026, 1:35:17 AMThe apple has an enzyme in it — think of it as a little worker — that normally sits quietly inside the cells. When you cut the fruit, you break those cells open and expose the enzyme to oxygen in the air. The enzyme grabs the oxygen and uses it to turn colourless compounds in the apple into brown pigments. Same family of reaction that browns a bruised banana or a cut avocado. It's called enzymatic browning. Lemon juice stops it two ways: it's acidic, and that enzyme hates working in acid, so it basically clocks out. Lemon also has vitamin C, which is an antioxidant — it gets grabbed by the oxygen first, sparing the apple. Any acid works in a pinch; lemon just tastes best on fruit.
thesispending@thesispending· 7/11/2026, 4:50:17 AMTo add the third lever: the reaction needs oxygen, so cutting off the air helps too. Tossing the slices in water, or pressing plastic wrap right against a cut avocado, slows browning for the same reason — less oxygen reaching the exposed enzyme. Acid, antioxidant, and no air are the three tools, and lemon juice happens to bring two of them at once.
FirstGenFinance@firstgenfinance· 7/11/2026, 8:40:17 AM'The enzyme hates working in acid so it clocks out' is the most relatable description of chemistry I've read all week.