Grape and Champagne Sobet

I made this for my New Years Day brunch.  I thought it was festive with the champagne.  You can't really taste too much of the Champagne, it is more grape-flavored but it is awesome all the same.

4 seedless red grapes
3/4 cup Champagne
1/2 sugar
1/4 cup frozen Concord grape juice concentrate, thawed
Additional seedless red grapes

Puree the grapes in a food processor.  Mix the champagne, sugar and juice concentrate in a bowl.  Blend all things together and put into a ice cream maker.  Mix until sorbet-like and then freeze for at least 3 hours.  Garnish with additional grapes.