Red cabbage as a pH indicator

September 21, 2026

Red cabbage contains anthocyanins, pigments that change colour depending on how acidic or basic a solution is. That makes the purple water left over from boiling cabbage a surprisingly good home-made pH indicator.

What you need

• A quarter of a red cabbage
• Hot water and a sieve
• Clear glasses
• Lemon juice, vinegar, baking soda, soapy water

Steps

1. Chop the cabbage, cover it with hot water and leave it for 15 minutes.
2. Strain the liquid. It should be a deep purple.
3. Pour a little into each glass and add one test substance per glass.

Results

Lemon juice and vinegar turned it pink-red, plain water stayed purple, baking soda went blue-green and soapy water leaned towards green. Adding vinegar to the baking soda glass slowly brings the purple back.

The liquid keeps for a couple of days in the fridge. After that it starts to smell like, well, old cabbage.