In a large bowl, toss together the berries. Spoon the berries into serving dishes and set aside.
Meanwhile, combine the egg yolks, sugar, grapefruit juice, and salt in a large metal or glass bowl. Whisk vigorously until combined and the color is a pale yellow. Set the bowl over a saucepan of simmering water. Be very careful not to let the bottom of the bowl touch the simmering water. Using a whisk or an electric hand mixer, vigorously whisk the egg mixture until it has tripled in volume and is very thick and creamy, about 4 to 5 minutes.
Spoon the warm zabaglione over the berries. Top with a light sprinkle of grapefruit zest. Serve immediately.