Dissolve yeast in potato water. Add sugar, and let stand five minutes. Add salt and beaten eggs. Stir in four cups of the flour. Add oil, stirring while adding. Stir in enough remaining flour to make dough that forms a ball and is not sticky. Put dough on a floured board. Cover with a towel and let rest 10 minutes. Knead 10 minutes. Put in a greased bowl, and let rise until it doubles (about one hour). Punch down. Braid to form two loaves and place on cookie sheets. Let rise again, approximately 50 minutes. Use a pastry brush to gently coat with a glaze made of a beaten egg and a few drops of water. Sprinkle the top with sesame seeds. Bake at 350°F until well done (approximately 45 to 50 minutes).