Bring 4 cups of pomegranate juice (a whole 32 fluid ounce bottle) to a boil.
Lower heat and bring juice to a slow boil until it reduces in half. You can let it reduce more than half if you want it to be a bit thicker. This process took about 15 minutes.
Stir in sugar until dissolved and remove from heat.
Pour into a glass jar and refrigerate.
Notes
Pomegranate juice is fairly popular and should be easy to find. POM is a popular but very expensive brand. I was able to find some 100% organic pomegranate juice for much cheaper.This grenadine won't be quite as red as Rose's, so you can add food coloring if you'd like just before bottling it. It will taste a million times better either way.Store grenadine in the refrigerator for up to two months.