Soak bread in a bowl of cold water for 4-5 minutes.
Put almonds and garlic in a food processor and blend till finely ground. Squeeze out the excess water and add the bread followed by the olive oil and the vinegar and blend till smooth.
Keep the processor running and pour in the cold water in a thin stream till fully incorporated.
Strain the soup through a fine sieve to extract as much liquid as possible. Season with salt, cover and chill overnight or for 3-4 hours at least.
Ladle soup into individual bowls adding equal quantities of grapes to each bowl. Drizzle with olive oil and serve.