- Combine the rhubarb, orange slices and sugar in a large glass bowl. Mix and mash with a wooden spoon until the ingredients are well combined.
- Cover and refrigerate for 2 days, mixing after the first day to continue incorporating the sugar into the fruit syrup.
- Strain the syrup into a clean 16-20 oz. jar
- Add the vinegar and spearmint, removing spearmint after 3 hours.
Shrub will keep in the refrigerator for several weeks. (If it lasts that long!)