Red cabbage, a variety of Brassica oleracea and a member of the Brassicaceae family, gets it’s color from anthocyanins. These water soluble pigments lend color to a variety of plants including many berries, beets, and purple tomatillos. I’ve long admired the vivid magentas produced, and equally long lamented that the color is not heat stable. Red Cabbage has a particular pigment from this group, flavin, which acts as a pH indicator.
I made sauerkraut for the first time tonight. After tossing the cabbage with salt and squeezing out the juices, the liquid turns from water-like to slippery, a good indication of a basic solution. The residual liquid remaining was still purple, but with strong blue undertones in contrast to the almost-red cabbage I started with. My suspicions of a present pH indicator were verified with a drop of vinegar.