How do you make jam with grape juice?

Making jam doesn't have to be difficult - blackcurrant jam is easy because it always sets. This recipe makes around 4.5kg (10lb) jam

1.8kg (4lb) blackcurrants

1.7 litres (3pt) water

2.7kg (6lb) granulated sugar

small knob butter

1 Leave the blackcurrants to soak in a sink filled with cold water. Pull them off their stalks and put into a preserving pan with the water. Bring to the boil and simmer, uncovered, for about 40 minutes, until the fruit is softened and the water reduced.

2 Add the sugar, stirring frequently until the sugar has dissolved, bringing it up to a gentle boil. Let it bubble for 10 minutes then test for a set - put a spoonful on to a chilled saucer then place it in the fridge for 5 minutes. Turn the jam right down in the meantime. The test should have set to a jam-like consistency if you push it with your finger. If not, return to the heat, re-boil then test again.

3 Add the butter, stir well. Cool the jam for 10 minutes to prevent the fruit sinking in the jar; ladle into sterilised jars - don't fill to the top. Let the jam cool before covering.