Warm the water and grape juice to about 115 °F and stir in the yeast. Let the mixture stand for about 10 minutes or until it is foamy. Stir in the salt, oil, and 2 cups of the flour, and beat it with a spoon or mixer until it is smooth. Add enough of the rest of the flour to make a soft dough. Knead the dough on a floured board for 10 minutes. Place the dough in an oiled bowl, turn it over so the top of the ball is also oiled, and cover it with a towel. Let it rise in a warm (85 to 90 f) place for about 45 minutes, or until it is doubled in volume. Shape the dough into a loaf, place it in an oiled 8 x 4 inch loaf pan, and let it rise in a warm place again for about 30 minutes, or until it doubles in volume. Bake at 425 °F for 10 minutes, then lower the oven temperature to 350 °F for an add