Blackberry jam

Makes 5 jars
Ingredients
2 lb (900g) blackberries
3 lb (1.4kg) sugar
½ bottle Certo
Method
- Use only fully ripe fruit.
- Crush thoroughly.
- Measure sugar and 2 lb. prepared fruit into a large preserving pan and
mix well. - Bring to a full rolling boil and boil over the hottest heat.
- Stir constantly before and while boiling.
- Boil hard for 2 minutes.
- Remove from the heat and stir in the Certo.
- Skim and stir by turns for just 5 minutes.
- Cool slightly to prevent fruit from floating.
- Pot and cover in the usual way.