Combine water, yeast, and 2 teaspoons sugar in a small bowl. Mix well; let stand 5 minutes or until bubbly.
Combine 4 cups flour, 1/2 cup sugar, salt, nutmeg, and lemon rind; add warm milk, melted butter, egg yolks, and yeast mixture. Beat until smooth.
Turn dough out onto a lightly floured surface; knead in enough remaining flour to make a stiff dough. Continue kneading 8 to 10 minutes or until dough is smooth and elastic.
Place dough in a greased bowl, turning to grease top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in bulk. Punch dough down, and place on a lightly floured surface. Sprinkle with citron, if desired, and knead until citron is evenly distributed. Shape dough into a cylinder 30 inches long.
Place cylinder on a greased baking sheet; shape into a ring, pinching ends together to seal. Place a well-greased 2-pound coffee can in center of ring to maintain shape during baking.
Press bean or pecan gently into ring from bottom so it is completely hidden by dough. Cover ring with a towel, and repeat rising procedure 45 minutes or until doubled in bulk.
Bake at 350° for 25 minutes or until golden brown. Remove coffee can and place cake on wire rack to cool. Drizzle cake with glaze; sprinkle with sugar crystals, alternating colors.