In a large bowl, combine yeast, 1/3 cup lukewarm water (105°F-115°F) and sugar. Let stand 5 minutes then stir until yeast dissolves.
In a small saucepan over low heat, melt butter, then remove from heat and let cool until warm. Add egg, orange zest, cinnamon, salt, mace, cloves, squash and butter to yeast mixture and stir until thoroughly mixed. Add flour 1 cup at a time to make a firm but not dry dough.
Turn dough out onto a lightly floured surface and knead vigorously 6 minutes. Coat a large bowl with cooking spray. Shape dough into a ball, add to bowl and turn to coat. Cover with a clean kitchen towel and let rise in a warm, draft-free place 1 1/2 hours or until doubled in bulk.
Lightly coat 9 1/4 x 5 1/4 x 2 3/4-inch loaf pan with cooking spray. Punch down dough and knead 1 minute. Shape into a loaf and place in pan seam side down. Cover with towel and let rise 45 minutes or until dough extends 1 inch above rim of pan.
Toward end of rising, preheat oven to 375°F. Brush top of winter squash bread with egg white and bake 35 minutes or until loaf is golden and sounds hollow when tapped on bottom.