If necessary, wash the strawberries, remove their stems, put in a porcelain bowl and cover with water, in which the citric acid has been dissolved. Leave the berries for a day to stand (covered), making sure to stir them regularly with a wooden spoon.

Next strain the contents through a moistened linen cloth. Weigh the juice and stir together with the same weight in sugar and add the preserving aid. Again strain the juice through the moist linen cloth, immediately decant into clean bottles and seal them with corks or rubber stoppers.