Stir the yeast mixture into the lentil mixture. Beat in 2 cups of the flour mixture. Stir in the remaining flour mixture, 1 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, 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.