In a small bowl, dissolve yeast in warm water. Let stand until creamy, about 10 minutes.
In a large bowl, combine the yeast mixture with 2 cups water, 3 cups flour, salt, sugar and vegetable oil; stir well to combine. Stir in the remaining flour, 1/2 cup at a time, beating well after each addition. When the dough has pulled together, turn it out onto a lightly floured surface and knead until smooth and elastic, about 8 minutes. Lightly oil a large bowl, place the dough in the bowl and turn to coat with oil. Cover with a damp cloth and let rise in a warm place until doubled in volume, about 1 hour.
Divide dough in half. Roll each half into a 9- x 12-inch rectangle and roll up jelly roll style, starting at long edge. Seal edges and place seam side down on a large baking sheet that has been sprinkled with cornmeal.
Use a sharp knife to slash each loaf diagonally 3 times. Brush with beaten egg white and sprinkle with sesame seeds. Cover and allow to rise 30 minutes. Meanwhile, preheat oven to 400°F (200°C).
Bake in preheated oven for 35 minutes, or until golden brown.