pour in water until just below the tops of the bottles. turn on the heat and simmer slowly. once they have reached this point, time them and process at a slow simmer for 20 minutes.
the cordial will rise up in the bottle and push out the air.remove the bottles carefully from the pan and tighten down the caps. as the cordial cools, it will sink back down the bottle and leave a vacuum at the top where no bugs can grow. 