Rinse and pick over the blackcurrants removing the stalks.
Pack them into a large Kilner type jar and squash them a bit with a potato masher to break them up and release the juice.
Add the cinnamon stick and pour in the vinegar.
Seal, shake and store in a cool dark cupboard for a week.
Set up a jelly bag or double muslin lined sieve and drain the fruity liquid overnight.
Measure the resulting liquid and for every 300ml/1/2 pint add 225g/8oz sugar.
Heat gently to dissolve the sugar then boil for 5 minutes.
Skim off any scum that floats on top.
Cool and pour into a pretty bottle.
Will keep for up to 1 year.