Mix the sugar and pectin together in a small bowl. Put the rhubarb purée in a saucepan and bring to the boil. Take off the heat and whisk in the sugar and pectin. Return to the heat and bring back to the boil, stirring continuously. Cook for 1 minute, then take off the heat. Spread out thinly on a non-stick baking mat using a step palette knife. Place in a dehydrator at 60