Combine the water, vinegar, coriander seeds, mustard seeds, allspice, cloves, and bay leaves in a small saucepan. Bring just to a boil, then reduce the heat to medium-low and simmer for 1 minute. Put the grapes in a heatproof bowl and add the warm pickling mixture. Let cool, then cover and refrigerate for at least 2 hours.
When you are ready to serve, drain the grapes and dry on paper t