I had purchased the purple grapes from Maradu wholesale market. It was fresh and price was also reasonable. Its an apt place to buy vegetables and fresh fruits. More about Maradu urban wholesale market.
I put the grapes for two hour in water sprinkled with salt and turmeric.
Washed them thoroughly
Boiled them in a clean vessel
I had no juicer so I blended the grapes and sugar using a mixie
Then strained it using a sieve or we may use a clean cloth
Chilled the juice
Serve them with great pride....