Extracted and refined from Red Cabbage. The red cabbage (purple-leaved varieties of Brassica oleracea Capitata Group) is a kind of cabbage, also known as Blaukraut after preparation. Its leaves are colored dark red/purple. However, the plant changes its color according to the pH value of the soil, due to a pigment belonging to anthocyanins.[1] In acidic soils, the leaves grow more reddish, in neutral soils they will grow more purple, while an alkaline soil will produce rather greenish-yellow coloured cabbages. This explains the fact that the 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 green/yellow in basic solutions. It can be found in all Europe, throughout the Americas, in China and especially in Africa. On cooking, red cabbage will normally turn blue. To retain the red color it is necessary to add vinegar or acidic fruit to the pot. - Quoted from Wiki