Anthocyanins Hydroxyl groups in the anthocyanin molecule found in red cabbage makes it very responsive to pH with acid environments shifting hues toward red and alkaline toward blue. A similar sensitivity can be observed by adding fruit juices with varying levels of acid to a glass of Concord grape juice. In strawberries a reduction in the number of hydroxyl groups renders the anthocyanin more stable, however, the extended heating, high pH, and prolonged storage of jams changes the bright red of a fresh strawberry to the dull reddish brown of a jam. In the kitchen avoid using aluminum pans or a worn knife as exposure to iron, aluminum, tin, and copper changes a red anthocyanin color to blue green or slate blue.