While rhubarb is more commonly paired with strawberries in pies, crisps and jams—something very interesting happens when you pair it with blueberries. The rhubarb transforms the blueberry jam into what taste like a mixed berry jam, without the need for a variety of expensive berries! The bitter acidity of rhubarb comes from its oxalic acid, which raspberries also happen to contain. This means that rhubarb takes on a slight raspberry flavor when added to the blueberries and the blueberries start tasting more like blackberries!?!🤯 Long story short—without expensive raspberries and blackberries or a lot of raspberry/blackberry seeds to strain out, you get a pretty decent mock mixed berry jam!