Rinse the cranberries and discard any bruised or shriveled ones.

Combine sugar and water in a medium saucepan, then bring the mixture to a boil over medium heat, stirring until the sugar dissolves.

Add the cranberries to the boiling sugar mixture, then reduce heat and simmer for about 10-15 minutes, or until the cranberries burst and the sauce thickens.

Remove the saucepan from heat and stir in the orange zest if desired.

Let the cranberry sauce cool to room temperature before serving; it will thicken further as it cools.