Kumquats are the original sweet-tarts! The "sweet" is in the skin, and the "tart" is in the juice. To experience the full spectrum of flavor, eat them whole, like grapes—peel and all. Try rubbing them gently between your hands before eating to release the sweet oil in their skin.
100g of kumquats (around 5 or 6) contain about 44mg (73% DV) of the antioxidant vitamin C, which helps prevent neurodegenerative diseases by removing free radicals. They are also chock-full of other polyphenolic flavonoid antioxidants such as carotenes and lutein.