Wash 500 grams of seedless grapes and remove them from their stems. Freeze the grapes for at least 4 hours or overnight.
In a small saucepan, combine 100 grams of sugar and 120 ml of water. Heat the mixture over medium heat, stirring occasionally until the sugar dissolves completely. Remove from heat and let the sugar syrup cool down to room temperature.
In a blender or food processor, blend the frozen grapes, cooled sugar syrup, and 1 tablespoon of lemon juice until smooth and creamy.
Pour the grape mixture into a shallow, freezer-safe container. Cover and freeze for at least 4 hours, or until firm.
Before serving, let the sorbet sit at room temperature for 5-10 minutes to soften slightly. Scoop into bowls or cones and enjoy!