Combine orange juice and zest, sugar, and vanilla bean in saucepan. Heat over medium high heat until mixture starts to boil, then continue cooking while stirring for about one minute until the sugar has dissolved. Thoroughly cool mixture in refrigerator 2 hours to overnight.
Strain mixture through fine mesh strainer and discard vanilla bean and excess zest.
Combine with buttermilk and process in ice cream maker. If your mixture is cold and the ice cream vessel is very frozen (I keep mine in the bottom of my deep freezer), the sherbet will be perfect after about 45 minutes.