Begin by gently placing the mulberries into a large bowl set in your sink. Fill the bowl with enough cool water to completely cover the berries (they’ll float a bit, but that’s ok). Add 2 cups of white vinegar to the berries and gently “swish” them around to ensure bugs and debris are knocked loose.

Carefully transfer mulberries to a colander and thoroughly rinse with cool water. Take care to be very gentle with the berries as they are very delicate.

After rinsing, allow berries to drain excess water for a few minutes.

Pour the rinsed and drained mulberries onto a rimmed baking sheet that has been lined with paper towels. If the berries are holding a lot of water, you may want to do this process twice, discarding the soaked paper towels and replacing with dry ones, if desired.

Ensure the mulberries are in an even, single layer and place the baking sheet flat in the freezer for at least four hours, or overnight, or until the berries have frozen solid. This is a process referred to as flash freezing.

Transfer the flash-frozen berries to a freezer-safe zip-top bag, labeling it with the contents, weight, and date of storage.