If using fresh pomegranates, start by slicing them in half, then juicing them using something like this cast iron juicer. It took 5 large pomegranates to yield 3 cups of pomegranate juice.
Add pomegranate juice, sugar, and lemon juice to a medium saucepan. Bring to a gentle simmer over medium heat until sugar dissolves, or about 10 minutes.
Lower heat and simmer, uncovered, until the mixture reduces to approximately 1 cup. It should have a syrupy consistency and coat the back of a spoon, which should take about an hour more. Skim foam, if necessary.
Remove saucepan from heat and cool completely. The syrup will thicken as it cools. If it's not thick enough, you can reduce it further. Transfer to a clean jar or fliptop bottle. It should keep for several months when refrigerated.
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Notes
Simmering the syrup can take anywhere from 50 to 70 minutes, depending on your stove and the size of the pot you use.
If juicing fresh pomegranates, keep in mind that pomegranate juice stains. You may want to wear gloves and an apron. Don't want to ruin your favorite shirt!
Is your syrup done? If you run your finger through the coated spoon, it should leave a trail. This will let you know that your pomegranate syrup is ready.
When stored in an airtight container in the refrigerator, pomegranate syrup can last up to six months.
Not recommended for waterbath canning, but you can freeze it for longer storage.