In large saucepan over medium heat add milk, sugar, and orange zest. Heat, whisking occasionally, until bubbles form around sides of pan and sugar dissolves, about 5 minutes. Transfer mixture to medium bowl and cool to room temperature, about 30 minutes.
Once milk mixture is cooled, add orange juice and pineapple. Cover bowl with plastic wrap and chill for 3 hours. Transfer mixture to ice cream maker and churn according to manufacturer’s directions. Serve sherbet soft of transfer to a 3 quart air-tight container and freeze until set, about 4 hours or overnight. Thaw sherbet on counter for about 10 minutes before scooping and serving.