Put the Port wine bittersweet, water, sugar and spices into a saucepan, bring to a boil and let reduce, over medium heat, for about 8-10 minutes. Leave to cool slightly.
Strain the syrup and pour over the grapes. Set aside.
In a serving glass, place stirred yogurt at the bottom and top it with grapes, pour a little syrup.
Decorate with some mint leaves.
NOTE: The syrup you get should not be dense.
** Marinated grapes in syrup will keep well for several days.
** The slice of ginger should not be too thick.
For celiacs: make sure all ingredients are gluten free.