Red cabbage and pH
Red cabbage is full of anthocyanin, a pigment that changes color with pH. It's pink-red in acid like vinegar or lemon juice, purple in plain water, and blue to green in baking soda water. Cabbage juice is basically a pH test strip you can eat.
Cook with acid to keep it red
Braised red cabbage stays bright magenta when you cook it with vinegar, lemon juice or apple. In plain tap water it fades to dull purple or blue. A splash of vinegar fixes it.
Test yourself
Questions from the interactive lesson, with the answer and the why.
You pour red cabbage juice into lemon juice in one cup and baking soda water in another. What do you see?
Lemon goes pink and baking soda goes blue-green. Acid shifts anthocyanin toward pink-red, and alkaline shifts it toward blue-green.
True or false: Adding a pinch of baking soda to the water you cook red cabbage in can turn it blue-green.
True. Baking soda raises the pH, which shifts the pigment toward blue-green.
What went wrong? You braise red cabbage in plain water. It comes out a dull blue-gray.
There was no acid, so the pigment drifted toward blue. Plain water lets anthocyanin shift toward blue. Add vinegar or apple to keep it red.
Fill the blank: The pigments in red cabbage that change with acidity are called ___.
The pigments in red cabbage that change with acidity are called anthocyanins. Anthocyanins turn red in acid and blue-green in alkaline conditions.
You want to know if a clear mystery liquid is acidic or alkaline. How does red cabbage juice tell you?
Pink means acid, and blue-green means alkaline. Anthocyanin color follows pH, so the juice works like a test strip.
Red cabbage juice color lab
A rainbow from one vegetable.
Do the 20-minute experiment