Sweet birch(black birch) twigs about thumb size and smaller chopped to 1 inch pieces enough to cover bottom of pot 2 to 3 inches deep. Just cover twigs with water and bring to just under a boil and remove from heat( hard boiling destroys flavor).let steep overnight.strain and reheat to almost a boil again next day adding sugar to make a syrup ( i like brown sugar). I always guess how much sugar…. If too sweet add more seltzer.if not sweet enough add more sugar. Very powerful flavor. Winter twigs only… summer twigs seem a little bitter..