Wash the grapes and spread them in a single layer on a clean kitchen towel. Pat the tops dry with a second towel, then let them air dry for at least 10 minutes. This step is important. Any moisture on the surface will cause the yogurt to slide right off.

Line a rimmed baking sheet with parchment paper. Make sure it fits flat in your freezer before you start dipping.

Spoon the Greek yogurt into a small bowl. If using the salt, stir it in now. Hold a grape between your fingers or spear it with a toothpick, dip it into the yogurt, and let any excess drip off for a second or two before setting it on the parchment. Work quickly but steadily through all the grapes.

Arrange the dipped grapes in a single layer so they are not touching each other. If they touch while freezing, they will stick together in a clump.

Slide the tray into the freezer and freeze until the yogurt coating is completely solid, at least 2 hours. Do not rush this step.

Once fully frozen, peel the grapes off the parchment and transfer them to a zip-top freezer bag. Press out as much air as possible, seal, and label with the date. Keep frozen for up to 2 weeks. Serve straight from the freezer.