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I've made fresh red cabbage (not canned or frozen) a few times. Back when I was still living with my parents, it always turned out fine. Now that I'm living on my own, I'm still using the same recipe, with one minor adaptation, which is leaving out the chunks of apple my mother always wanted me to add. I've never been a fan of those chunks, and I prefer eating mine with apple sauce, added after cooking.

But now, when I cook the red cabbage, it suddenly (and always) turns blue. The taste is still pretty much the same, it's just a colour difference. Still, I'm wondering what causes it, and if there's anything I can change to get it to look red again?

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    Fun fact: you can use the properties described in the answers below to do a nontoxic science demonstration for kids. Take a leaf or two of red cabbage, cut it up, then cover it with water in a pot (just an inch or less should be fine) and bring it almost to a boil, then shut off the heat. This extracts the pigment, which you can use as a pH indicator, changing the color with baking soda or lemon juice.
    – fyrepenguin
    Commented Jan 27, 2022 at 6:12
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    @DrakeP Sorry, I finished it all. Otherwise I couldn't have dessert!
    – Tinkeringbell
    Commented Jan 27, 2022 at 8:00
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    @Tinkeringbell haha that's ok, I googled some pictures 😄 happy cooking!
    – Drake P
    Commented Jan 27, 2022 at 8:03
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    If you're using processed red cabbage (e.g. frozen, canned, pickled etc) it might contain food colouring.
    – Graham Laight
    Commented Jan 28, 2022 at 9:27
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    add some dish soap to turn it green.
    – Tschallacka
    Commented Jan 28, 2022 at 10:50

3 Answers 3

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The red in red cabbage is Anthocyanin, which is a natural pigment which turns blue in the presence of a base. Apples are slightly acidic, adding apples kept the cabbage's ph towards the acid side, keeping it red.

Adding a squeeze of lemon juice will do the same thing as apples.

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    It's worth noting that "Anthocyanin" had absolutely no connection with cyanide: see Wikipaedia for the Greek derivation.
    – Mark Morgan Lloyd
    Commented Jan 27, 2022 at 10:00
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    Also, the water used has an effect. The acidity of household water can vary considerably (to the point of things like not being able to cook legumes or potatoes). Blue cabbage is a brilliant indicator.
    – Luaan
    Commented Jan 27, 2022 at 11:01
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    vinegar would also be a good source of acidity if you'd prefer no citrus taste
    – Tristan
    Commented Jan 27, 2022 at 16:28
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    In Germany there are two words for it blue and red cabbage. This stems from the traditional recipes being acidic or not.
    – Portree Kid
    Commented Jan 28, 2022 at 9:00
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    @Luaan, why would you not be able to cook certain things when the acidity of tap water is 'wrong'?
    – Holloway
    Commented Jan 28, 2022 at 11:57
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It's turning blue because it's no longer acidic - the apples in your parents' version was providing some acidity which keeps it red.

You can sub in something else to provide the acidity if the apple pieces aren't desired (vinegar or a little lemon juice should do the trick).

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Red cabbage is an indicator that changes color depending pH. If in acidic environment, the cabbage changes color to red, in an alkaline environment it turns blue.

Depending on the acidity/alkalinity of your water the cabbage can turn red or blue. This can be seen in the naming from different regions: It's called „Blaukraut“ (blue cabbage) in southern Germany, and in the northern part it’s called „Rotkohl“ or „Rotkraut“ (red cabbage).

By adding acids like vinegar or apples you can influence the color.

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    And in the south, in Austria, it is "Rotkraut" again :-)
    – Gerda
    Commented Jan 27, 2022 at 14:33
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    For the German speakers here: Exactly the question what red cabbage is called locally is part of the current (13th) round of the research project Atlas der deutschen Alltagssprache. In case you want to contribute.
    – Stephie ♦
    Commented Jan 27, 2022 at 20:54
  • Thanks, Stephie, I was not aware there is such a thing. I‘ll surely contribute
    – jmk
    Commented Jan 27, 2022 at 21:48

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