Pour the sugar and water into a saucepan and place on the heat. Cook for 2-3 minutes or until the sugar dissolves. Let the mixture cool down and put the container that you will use to prepare the sorbet into the freezer. Peel the kiwis and mash them with an immersion blender. Take the syrup, which will be cold by now, and mix it with the kiwi puree; take the container out of the freezer and pour in the kiwi and sugar mixture. Put the container back into the freezer: remember to take the container out of the freezer at regular intervals of 30 minutes to stir the mixture with a spoon, so that the surface does not crystallise. Repeat at regular intervals for at least four hours. The sorbet must appear creamy and without sugar crystals: if necessary, leave the sorbet in the freezer for several hours (the timing is indicative, it depends on your freezer), mixing the sorbet often.