Put the sugar in a saucepan with the cinnamon stick and a scant cup of water. Bring to a boil and simmer until the sugar has dissolved completely and the syrup is clear. Remove the cinnamon stick and let the syrup cool. Mix together the sugar syrup, red wine and orange zest. Beat the egg white until soft peaks form, and then fold into the red wine mixture. Transfer the mixture to a metal bowl and place in the freezer for 3 hours. Break up the ice crystals occasionally by whisking with a balloon whisk. Before serving, the sorbet should be whisked again, then divided between chilled glassed. Decorate with mint leaves.
Variation: The sorbet can also be served in tall glasses, which are then topped up with chilled Spanish sparkling wine (Cava).