Start by rinsing your fresh cranberries under cool running water in a colander. Pick through the berries to remove any that are bruised, soft, or shriveled. Discard any small stems that might still be attached to the fruit.
Place the cleaned cranberries into the basin of your slow cooker. Add the sugar, orange juice, water, and orange zest. Toss in the cinnamon stick and stir everything together until the sugar is somewhat distributed among the berries.
Cover the slow cooker with its lid. Set the temperature to high and cook for 3 hours. If you have more time and want a slower process, you can cook it on low for 6 hours. You will know it is ready when the cranberries have popped and the liquid has turned into a deep red syrup.
Once the cooking time is complete, turn off the heat and remove the cinnamon stick. Stir in the alcohol-free vanilla extract. If you prefer a smoother sauce, use a potato masher or a large fork to crush some of the whole berries against the side of the pot. The sauce will continue to thicken significantly as it cools.
