Wash the grapes and boil with water for some 15 minutes and mash with a wooden masher.
Mash nicely and filter the content and again bring it to boil.
Let it boil for 5-10 minutes.
Then again strain it.
In between keep water boiling add sugar and citric acid and let it boil for some time(20 minutes).
Then filter the content(sugar syrup) and add to the grape juice,mix well.
Filter it once again.
Let it cool and store.
For making juice:
Add required syrup to a glass,add icecubes and water mix and enjoy.
Notes
I have not added sodium benzoate if necessary you can add.
Store it in sterilized bottles in fridge.
I have filtered grape juice two times to get clear extract.