Dissolve yeast and the 1/2 teaspoon sugar in the warm water. Set aside.
In a large mixing bowl beat eggs with an electric mixer until frothy; gradually beat in the 2/3 cup sugar. Beat in orange peel, orange juice, melted butter, oil, anise seed, and salt. Beat in 2 cups of the flour and the yeast mixture; beat on high speed for 3 minutes. Using a wooden spoon, stir in as much of the remaining flour as you can.
Turn dough out onto a lightly floured surface. Knead in enough remaining flour to make a moderately soft dough that is smooth and elastic (3 to 5 minutes). Shape into a ball. Place in a lightly greased bowl, turning once to grease surface. Cover; let rise in a warm place until double (about 2 hours).
Punch dough down; cover and let rest 10 minutes. Press dough evenly into a greased 10-inch tube pan. Cover; let rise in a warm place until almost double (1-1/2 to 1-3/4 hours).
Preheat oven to 300 degree F. Bake bread about 50 minutes or until top and sides are golden brown. Remove from pan; cool on wire rack. Makes 1 loaf (16 slices).