Wash the apples, peel, core and cut up. Bruise the root ginger, tie in a piece of muslin with apple peel and cores. Put the apples, water, lemon juice and muslin bag into a preserving pan and cook until apples are tender. Remove muslin bag, squeezing gently to extract pectin. Add sugar and chopped crystallized ginger. Put over a low heat until sugar has dissolved, then boil rapidly until setting point is reached. Pour into hot sterilized jars and cover tightly.