Take one carrier back of small, sharp grapes with pips (so not very desirable in the raw).
Wash the grapes and remove stalks, bad grapes and any other undesirables (especially those with legs).
Add cold water to a depth of 1cm and cook gently to release juice from grapes.
Allow to cool slightly and blitz with a stick blender.
Strain through muslin overnight. In the morning squeeze out the last of the juice.
Finely chop a red chilli!
Add 1 kg sugar and pectin. Bring to the boil.
If unable to find the sugar thermometer then test periodically on a cold saucer until the jam 'wrinkles up' when pushed with a little finger.
Strain through a fine sieve into a large measuring jug.
Bottle up in clean jars and be sure to seal whilst still around boiling temperature.
Once a jar is open store in the fridge.