Place the cranberries in a colander and run them under cold water, gently rubbing them with your hands to remove any debris.

Pour 6 cups of water into your large saucepan and add the rinsed cranberries. Use a wooden spoon to stir gently and distribute the berries evenly throughout the water.

Place the saucepan over medium-high heat and bring the water to a rolling boil, which takes about 5 to 7 minutes.

Once boiling, lower the heat to medium and let the mixture simmer gently for 12 to 15 minutes. The cranberries will start to pop and split, and the water will transform into a deep red color.

Remove the pot from heat and let it cool for 5 minutes, then carefully pour the mixture through a fine mesh strainer set over a large bowl, pressing gently on the berries with the back of a spoon.

Pour the strained juice back into the saucepan and stir in your chosen sweetener, starting with 1/2 cup and adding more to taste.

Transfer the sweetened juice to clean glass jars and let it cool to room temperature on the counter, about 15 minutes. Then place it in the refrigerator until completely chilled, at least 2 hours.

Pour the juice over ice cubes and serve immediately, or mix with sparkling water for a lighter spritzer version. Store any unused juice in sealed glass bottles in the refrigerator for up to two weeks.