Peel, core and dice pineapple. In a food processor combine pineapple with 1/4 cup sugar and lemon juice and process until smooth. (This may need to be done in batches.) Add more sugar if necessary. Transfer mixture to ice cube trays or metal shallow baking pan, cover with plastic and freeze until almost frozen. In processor add frozen pineapple and process, in batches, until smooth. Transfer to plastic container and freeze, covered, until solid.