Peel the beets - cut each into eight wedges, and add to a 1-quart jar along with the ginger, mustard seeds and bay leaf.
In a saucepan, combine the vinegar, maple syrup and salt with 1 cup of water. Stir to combine and bring to a boil over medium heat. Pour enough liquid into the prepared jar to cover the beets and let cool to room temperature.
Refrigerate for at least 12 hours and up to 2 weeks, shaking the jar every few days to distribute the flavors. Makes 1 quart.