I could be a very good start. I would add other ingredients.I would use the grapes for a good source for liquid and yeast for ferment.
There's a bunch of recipes out there. I'd see what's available locally for free or very cheap that's being thrown away from farmers or vendors. Variety for various nutes. High on my list are beets and nanners. I like beets for the antioxidants and micro nutes
Mango
Papaya
Apple
Carrot -
Zucchini
Squash
Banana
Beet
Small watermelon or in your case grapes
I'd press the grapes and use the juice to blend some of the beet, apple and carrot. Chop all the other ingredients into a chunky salsa consistency..
Ideally, use equal amounts, but it's not that exact kinda thing. You want a very wet chunky slurry. Weigh and add the equal amount of brown sugar and mix it all together. very well. I use the unprocessed raw sugar. The sugar will draw out the juices. Just cover with a towel and keep in a warm place. I stir every few days. You can start using in about two weeks, just take a little and let the rest continue to ferment. I put a sugar cap on top after pulling off some juice, but it's not required. It keeps the product 'sealed'
The end product is kinda like a thin syrup and pretty powerful.
I think the next batch I make, I'm gonna add another ingredient. I think I could add a fair amount of freshly malted barley that would add some interesting hormones to the mix. I think it would an interesting addition.