Around the middle of July when the grapes are formed and beginning to lose their strong green colour although not their acidity, pick sufficient for your needs. Blanch them briefly and spread them out to dry before crushing them, pushing the liquor through a sieve. Leave the juice to settle then pour it through a paper filter into sterilized bottles. To prevent any fermentation, some cooks recommend filling the top inch of the bottle with a layer of oil to exclude the air before inserting tight-fitting corks. Always store the bottles in a cool place.