Quarter the apples, leaving the skins on and the cores in. Chop mint leaves roughly. Put apples and mint into a large saucepan. Cover with cold water and bring to the boil. Simmer until thoroughly cooked. Put the mixture into a jelly bag over a large basin and drain overnight. Measure the liquid and add lib sugar for every pint. Turn into a large saucepan, add sugar and bring to the boil. When sugar is dissolved, boil rapidly until the jelly reaches setting point when tested on a cold saucer. To improve colour, a few drops of green colouring may be stirred well in at this stage. Pour the jelly into clean, hot jars. Leave until cold then cover and seal.