Let the coffee and water simmer gently for about 20 minutes. Strain the liquid with filter paper or cotton cloth. Mix the concentrated coffee with the sugar in a saucepan, bring to the boil again and simmer for about 8 to 10 minutes so that the sugar caramelizes.
Pour the syrup into hot rinsed glasses or bottles. The syrup thickens as it cools. You can also mix in a small glass of rum.