Mountain ash jelly, also called rowan berry jelly, is jelly made from the berries on a mountain ash, or rowan, tree. Mountain ash berries are generally only edible after some form of processing, due to their chemical composition and inherent bitterness.
Mountain ash trees, which are commonly found in North America and Europe, produce clusters of orange or red berries that are high in vitamin C. The trees are typically able to thrive in extreme temperatures. Some of the berries' strong taste comes from their chemical content, which includes parasorbic acid, malic acid and cyanidic properties. Processing the berries through cooking or freezing reduces the unpleasantness of these properties.