This lime sorbet is infused with kaffir lime leaves and zest. Lime juice is also used, but you need to use ordinary limes for this, as kaffir limes are used mainly for their aromatic zest and leaves — they have virtually no juice.
For added flavour, the grated zest is mixed with sugar and set aside for a day. The sugar, being hygroscopic, will pull out the essential oils in the zest, and these will absorb into the sugar. This method will extract more flavour than by simply placing the zest in water.