In a medium, nonreactive bowl, combine the strawberries and rhubarb. Pour sugar on top and mix until sugar coats all 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.

Mash fruit again until it is mushy. 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, making sure to stir the mixture every day.

After a week, strain the fruit by pouring through a cheesecloth-lined sieve. Save the liquid in a sterilized Mason jar for up to 6 weeks in the refrigerator.