In a small saucepan, combine all the ingredients for the marinade.
Bring it to a boil and whisk it a few times to let the sugar dissolve completely. Once boiling, lower the heat and simmer for 1 minute. Turn off the heat. Set aside to cool completely.
Place the eggs in a plastic bag and add the marinade to the bag. Why am I recommending a plastic bag? With a plastic bag, we don't have to use a lot of marinade to submerge the eggs. This marinade is used only one time for food safety reasons, so it's most economical to prepare no more than the amount you need. If you use a container instead of a bag, it requires more marinade to submerge the eggs.
Remove the air from the bag and use a clip or rubber band to seal the bag right above the eggs. This way, the eggs are completely submerged in the marinade. Refrigerate for 8 hours or overnight. You can rotate the eggs occasionally if you like.