Why is my red cabbage suddenly turning blue when cooking, while it never did so before?

Question

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?

Answer 1

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.

Answer 2

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).

Answer 3

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.