With a sharp vegetable peeler, carefully peel all the zest from the tangerine, lemon, orange, and lime, and half of the grapefruit zest. Be sure to take only the colored peel and none of the bitter white pith. If you do end up with some pith on the strips of zest, remove it with a sharp paring knife. Bring a small pot of water to a boil and parboil the citrus zest for 3 minutes. Drain well and cut the strips into a thin julienne. Squeeze the juice of ½ of each fruit and mix together.

Bring the fish stock to a boil and reduce to ⅓ cup. While the stock is still hot, mix it with ⅓ cup of the fruit juice and whisk in the olive oil. Season with salt and pepper and add 3 tablespoons of the julienned zest. Keep warm but not hot, lest the fruit juices lose their fresh flavor. 

Make a fire in the grill and let it burn down to a bed of hot coals. Season the salmon with salt and pepper. Clean the grill well with a wire brush and then oil it with a clean rag and olive oil. Oil the fish well and grill from 3 to 4 minutes on each side, depending on the thickness of the fillets. The salmon should be just set but still a little translucent at its center. Arrange on a plate and spoon the sauce over, distributing the zest evenly around.

Serves 6. 

* Chez Panisse Fruit by Alice Waters is available to purchase at the Ecology Center Store