Red cabbage changes colour (anthocyanins)
Also searched as: red cabbage blue, blue cabbage, red cabbage colour, anthocyanins
In short: The red pigments in red cabbage, berries and red onions change colour depending on acidity: red when acidic, purple when neutral, blue when alkaline.
Like a natural acid test: red cabbage tells you by its colour how acidic your pot is.
acidic: red
What happens
Anthocyanins are pigments that change shape with the . In acidic surroundings they are red, neutral purple, and in alkaline surroundings blue to greenish. Hard, chalky water therefore often turns red cabbage bluish; a splash of vinegar or some apple turns it red again.
Why it matters
That is why some German regions call it red cabbage and others blue cabbage. And it is why apple and vinegar belong in the recipe.
Rules of thumb
- For a bright red: add vinegar, wine or apple.
- Red berries in batters with baking soda can turn greenish.
Levers
In practice
Vegetables
Braise red cabbage with apple and vinegar: colour and flavour in one.
Cakes and baking
Blueberry muffins with a lot of baking soda get greenish spots.
- Harold McGee: On Food and Cooking (2004), Kapitel Gemüse, Eier