Kitchen Science – cabbage pH indicator

This one’s a favourite in our house. Any time we have red cabbage, we keep the ‘juice’ and use it to test wether things are acid or alkaline, often with some surprises. Certainly makes for a good conversation starter about why kids should brush their teeth after a meal!

First, the science. Red cabbage contains a pigment called anthocyanin, which changes colour when exposed to acid or alkaline. Acid (pH1) will turn it red. Alkaline will turn it green (pH14). Neutral (pH7) in the middle is purply-blue. And there’s a spectrum in-between.

Preparation is pretty simple. Just chop up a red cabbage, steam it (you can just boil it too) and collect the juice.

We like to pour some into a row of glasses and then arrange them on a scale from acid to alkaline. As you can see, we live in an area with relatively alkaline water. Yours may be more blue/purple when it starts out.

Here’s what happens when you put some vinegar (acid) in. It changes colour within seconds.

And here’s the result of our latest session…

In order from acid to alkaline:

1. Apple juice
2. Lemon
3. Pan scouring cream
4. Vinegar
5. Beer
6. Baking Powder
7. Surface cleaner
8. Bicarbonate of Soda

Which is pretty consistent with a quick Google search. The beer and the apple juice were a bit of a surprise!

And don’t waste that cabbage, it’s amazing stuff!