How do I stop red cabbage turning blue or grey?
Red cabbage is a pH indicator, which is why it changes colour in the pan. Add acid and it stays red; British tap water and a long cook turn it blue.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 3 min
Short answer
Add something acidic at the start — cider vinegar, red wine vinegar, apple, red wine or the juice of an orange. The anthocyanin pigments in red cabbage are red in acid, purple around neutral, blue in mild alkali and green in strong alkali, and hard tap water in much of Britain is alkaline enough to turn it blue over a long braise.
This is the same chemistry as the school experiment where red cabbage water is used to test household liquids, and it is happening in your casserole for exactly the same reason. Traditional braised red cabbage recipes all contain vinegar or apple, and that is not just for flavour.
Step by step
- Add the acid at the beginning, not the end.Two or three tablespoons of cider or red wine vinegar per medium cabbage, going in with the cabbage rather than stirred through at the end. The pigment needs to be in an acidic environment throughout the cook, not acidified afterwards.
- Use apple, orange or wine as well as or instead of vinegar.A grated Bramley or two eating apples, the juice and zest of an orange, or a glass of red wine all supply acid along with flavour and sweetness. This is why the traditional braised red cabbage combination exists.
- Balance the acid with sweetness.Brown sugar, redcurrant jelly, apple or a spoonful of marmalade. Enough acid to hold the colour will taste sharp on its own, and the sweet-sour balance is the point of the dish.
- Watch out for hard water and bicarbonate of soda.Alkaline tap water shifts the pigment towards blue over a long braise. If your water is very hard and the colour keeps going, use a little more vinegar or cook it in wine and juice with very little water. Never add bicarbonate of soda to red cabbage — it turns it a decisive blue-green.
- Mind the pan.Anthocyanins react with iron and aluminium, which can dull the colour and add a metallic taste. Stainless steel, enamelled cast iron or a non-reactive casserole is the right choice for a long braise.
- Cook it long and slow for a braise, or fast for a slaw.Braised: 45 minutes to two hours, covered, low heat, until soft and glossy. Raw for a slaw: shred finely and dress with a sharp vinaigrette, which both softens it and fixes the colour. There is no useful middle ground — a briefly boiled red cabbage is neither.
- Expect it to bleed and plan around it.Red cabbage leaches colour into anything alongside it. Cook it separately from potatoes and pale vegetables, and be aware it stains chopping boards, wooden spoons and hands.
Tips
- Braised red cabbage is better the next day and freezes very well, which makes it one of the best make-ahead components of a Christmas dinner.
- A cinnamon stick, a few cloves, star anise or juniper berries all suit it, and they are traditional partly because they stand up to the vinegar.
- If a batch has gone blue, a good splash of vinegar stirred in will shift it back towards purple — the colour change is reversible with pH, unlike chlorophyll.
- Keep the cabbage covered while braising so it steams in its own liquid rather than drying out; unlike green vegetables, a lid is right here.
Questions people ask
Why does red cabbage go blue in a stir fry?
Usually because there is nothing acidic in the pan and it has been in contact with a wok or with alkaline water. A splash of vinegar or lime at the start fixes it.
Is blue red cabbage safe to eat?
Completely. It is a pH effect on a pigment and nothing more. It just looks unappetising.