The red cabbage (Brassica oleracea var. capitata f. rubra) is a sort of cabbage, also known as Red Kraut or Blue Kraut after preparation. Its leaves are coloured dark red/purple. However, the plant changes its colour according to the pH value of the soil, due to a pigment called anthocyanin.
On acidic soils, the leaves grow more reddish while an alkaline soil will produce rather greenish-yellow coloured cabbages. This explains the fact that the very same plant is known by different colours in various regions. Furthermore, the juice of red cabbage can be used as a home-made pH indicator, turning red in acid and blue in basic solutions. It can be found in Northern Europe, throughout the Americas, and in China.
On cooking, red cabbage will normally turn blue. To retain the red colour it is necessary to add vinegar or acidic fruit to the pot.
Red cabbage needs well fertilized soil and sufficient humidity to grow. It is a seasonal plant which is seeded in spring and harvested in late fall. Red cabbage is a better keeper than its "white" relatives and does not need to be converted to sauerkraut to last the winter.