To preserve the grapevine leaves, harvest when pruning back a vine that is full of healthy leaves. Cut the stems and then remove each leaf from the stem. Then remove the leaf stalk from each of these leaves. It is a little fiddly but worth the result as you will then have a pile of flat vine leaves, without stringy stalks or the stringiest leaf veins attached.
Stack them in piles of perhaps 10 leaves, each laid flat. Do this after checking that each is clean and not harbouring any insects.
Then roll each pile of leaves individually, into a tidy rolled package. Do this by firstly folding up the pointed ends, towards the centre. Then roll fairly tightly, with the edges of the leaves neatly tucked inside.
With each of these rolls, as you make them. add them to a sterile glass jar. One that is tall enough so that when the rolls stand up within the jar, there is a little headroom, which will be full of salt water. I use 200 - 400ml jars, depending upon my leaf harvest.
Fill the jar with your rolls of flat, de-stalked vine leaves. So they will be standing up neatly, and hopefully you jar will be packed with them. Now make the saline solution.
Now pour the saline carefully into your leaf-roll filled jars. Without damaging the rolls, poke around a little to release any air bubbles, and then top up to the brim of the jar. Remember there should be some space above the rolls for the saline. This ensures that the leaves are not in contact with air, as this will spoil the fermentation process and can spoil the food.
Now close the lids of the jars. Label with the contents and date of set up. Then leave at room temperature for a few weeks so that the leaves can gently lacto-ferment in the salt water.
Burp the jars daily, especially the first days or in hot weather. Ideally use jars with pressure release seals also.
If you want to speed up the process, you could hot salt brine the leaves. To do this we use hot salty water. Simply dissolve 3g-5g of salt in a litre of hot water. Add the salt to water from a hot kettle or add both salt and water to a pan and bring to the boil.
When the salt water is boiling hot, turn off the heat and place your jars on the base of a saucepan and pour in the hot salt water. As before, ensure all air is out of the jars, poke gently between the rolls, get all trapped air out and be sure to top up the jars. Now you need to heat the jars for a while. I prefer to do this by adding some plain water to the pan, around the filled jars, and then simmer gently for about 20 minutes. Then allow them to cool and store. Fermentation will not happen in the salt brined jars, the heat and salt will destroy any microbes which were in there and they should keep in the fridge for some months.
The lacto-fermentation method will continue to develop flavour over the coming weeks, so check it now and them to see how you like the taste. When you are satisfied, store in the fridge.
See the general guidance on lactofermentation and safety.