So today is the day we make VERJUS aka verjuice in English, ie the extremely tart juice of unripe grapes; this is what they used, in the Middle Ages & afterwards, all over Europe when they couldn't get their hands on lemons (ie for Northeners, most of the time).
You need a good quantity of the aforementioned unripe grapes (pea-sized) and a juicer, the centrifuge kind not a blender because otherwise you'll have to sieve it & that would be tedious).
Juice the grapes, pour the murky looking liquid into freezer bags, freeze it. I freeze a 1/4 litre at a time. Once frozen it separates into a green sludgy looking layer and a clear watery layer, this is normal & doesn't affect subsequent use.
What subsequent use I hear you ask - well here it is, LA recette du poulet au verjus (& v delicious it is too).
You need: chicken (legs cut in two are fine, thighs are best, a couple for each diner). 2 or 3 onions, chicken stock (a good glassful), verjus (the 250ml lump from the freezer, or fresh if you are doing it now), salt, some duck fat.
Slice up the onions thinly (use a mandolin & don't chop off your finger-ends).
Heat up a biggish pan, melt the duck fat, fry the salt-sprinkled chicken all over until it is nice & golden-brown & the skin looks appetizing, add the onion & keep cooking & stirring it about until the onion is translucent & semi-disintegrated. Pour in the stock, a glass or so will do. Then add the verjus and let it simmer, possibly with a lid half-on. Eat it with pommes sarladaises and a salad.
The juice will look vile but it is delicious.