Although rhubarb is often classified as a fruit, it is actually a vegetable. Only the (red) stalks of rhubarb are eaten. The stalks are cooked until they fall apart into fibers. Rhubarb contains a lot of oxalic acid. Due to its sour taste, a lot of sugar or honey must be added during preparation. Rhubarb can be served as a side dish or dessert, but it also works well in the well-known pies and tarts.