In a medium, nonreactive bowl, combine pomegranate arils and sugar; mix until the sugar coats all the fruit. Let mixture sit for 1 hour at room temperature.
Mash fruit with a wooden spoon to break it up.
Let sit for another hour and stir again. Cover with a clean kitchen towel and let sit at room temperature for 24 hours.
Add in vinegar, stir, and let sit, covered, for 1 week at room temperature, making sure to stir the mixture every day. After a week, strain the fruit by pouring through a cheesecloth-lined sieve.