Tip the grapes into a large saucepan set
over a low heat, then cover and leave to
gently cook for 5 mins until the juices start
to run. Take a potato masher or fork and
mash up the grapes. Leave to cook for about
10 mins more, mashing every now and again
until the grapes are falling apart. Place a
clean tea towel or kitchen cloth in a sieve
set over a bowl, then pour the grape mixture
into this. Let the mixture drip through for at
least 1 hr or preferably overnight.
Measure out the juice (you should have
about 600ml) and pour it into a pan along
with the sugar and lemon juice. Set the
pan over a high heat and bring to the boil.
Skimming any scum as it boils, let the
mixture bubble until the temperature reaches
105C on a sugar thermometer. If you don’t
have one, put a small plate in the freezer for
5 mins, then pour a little of the juice onto
the cold saucer. After 1 min, run your finger
through; if the jam wrinkles slightly, it’s ready.
Pour the hot jam into a sterilised jar. Will
keep unopened for up to 3 months.