The fruit adds its distinctive flavor to sorbet.
In a large saucepan, combine pears and 1 cup sake. Bring to a simmer over medium heat; cook, covered, until pears are tender when pierced with the tip of a paring knife, 30 to 35 minutes.
Transfer pears and cooking liquid to a food processor. Add sugar, and process until smooth. Add lemon juice and the remaining 1/2 cup sake; pulse to combine. Transfer mixture to an airtight container, and refrigerate until completely chilled, at least 2 1/2 hours.
Pour mixture into an ice-cream maker, and freeze according to manufacturer's instructions. Transfer sorbet to an airtight container; freeze at least 2 hours or overnight before serving.