Place wineberries in a sterilized glass quart container with a lid.
Muddle the berries with a muddler or the handle of a wooden spoon until they are all smashed.
Add vodka to the container, filling to the top.
Cover the container and place in the refrigerator or a cool, dark place for 3 weeks.
Strain the cordial through a fine-mesh sieve. Discard solids.
Bring sugar and water to a boil, stirring.
Add sugar syrup to the cordial, a little at a time, until cordial is sweetened to your liking. (You'll want to use at least half of the sugar syrup.)
Return cordial to container and store covered at room temperature.
