They are many methods to preserve vine leaves, for me, the best is in brine. I know a lot of people freeze them but they discolour and crumble.
The best time to pick fresh vine leaves in Greece and Cyprus is from April till May when they are fully grown and tender, but in the UK, it’s from June through August.
Method:
Wash the leaves and dry them, cut stems, and roll in bundles, 10 leaves at a time.
Place the bundles tightly in sterilised jars; put as many rolls as the jar will take.
For each jar, place one jar of boiling water in a measuring jug with one tablespoon of coarse salt and 1/2 tablespoon citric acid, or 2 tablespoons of bottled lemon juice. Stir to dissolve and pour into the jar containing the vine leaves – fill it all the way to the top with the hot brine.
Screw the jar lids tightly, turn the jars upside down on a tea towel or on some foil, and leave until they cool completely.
Turn the jars the right side up, label and store in a dark place. They should keep for one year or longer.
When ready to make your Ντολμάδες (Dolmathes) / Κουπέπια (Koupepia), wash the leaves in warm water.