Combine the almonds and garlic in a blender or food processor and blend until the almonds are very finely ground, almost pastelike. Meanwhile, soak the bread in cold water, then squeeze out the water. Add the bread to the blender and blend until smooth. With the motor running, pour in the oil in a thin stream, then add the vinegar, scraping down the sides often. Pour in the grape juice and iced water 1 cup at a time. Season with salt. Chill in the refrigerator, at least 6 hours. The soup should be very cold. Serve in chilled soup bowls and garnish with the grapes.