Wash the blackberries and remove any stems and unripe fruit. Put into a pan with just enough water to cover, and the acid. Bring to the boil and simmer gently until the fruit is soft. Put through a sieve and weigh the pulp. Allow 1lb/450g sugar to each 1lb/450g fruit pulp and stir in the sugar over low heat until dissolved. Bring to the boil and then cook gently until thick, stirring well. Pour into small hot, wide-necked jars, and cover.
© 1978 Mary Norwak estate. All rights reserved.