Wash, dry and sort the berries and place in a tall saucepan. Add the cinnamon stick, port wine and sugar, bring to the boil. Grate the lemon zest and let it simmer for 5-7 minutes. Skim off the resulting foam a little.
Remove the cinnamon stick, lightly mash the fruit.
Pour into hot rinsed glasses and turn upside down for 5 minutes.