In a medium saucepan, combine the cranberries, sugar, water, cinnamon stick, and orange zest.
Bring to a boil over medium heat, then reduce the heat to maintain a gentle simmer. Cook at a gentle simmer until the cranberries are just beginning to split, and the liquid is red, 8 to 10 minutes. Don't cook for longer than 10 minutes.
Remove the saucepan from the heat and let the mixture steep for 5 minutes.
Strain through a fine mesh sieve. Let the syrup cool completely before refrigerating.
Notes
Don't overcook--Don't simmer the syrup for longer than instructed in the recipe. Cranberries are very high in pectin, and if you cook it too long, you'll end up with cranberry sauce.
Storage and freezing--Store in a sealed container in the fridge for up to 1 month or freeze for up to 3 months.
Scaling--The recipe can be doubled or tripled easily.
Dietary--This recipe is suitable for gluten-free, dairy-free, and vegan diets.