Step 1

Fill a large pot with water, cover and bring to a boil. Add the canning jars, lids and rings along with a set of tongs and a ladle and simmer over low heat for about 10 minutes to sterilize. Cover the pot and turn off the heat.

Step 2

Set a metal rack in another large pot. Fill the pot with water, cover and bring to a boil.

Step 3

Meanwhile, in a saucepan, combine both vinegars with the brown sugar and salt and bring to a boil to dissolve. Using the sterilized tongs, remove the jars from the hot water and transfer them to a rimmed baking sheet.

Step 4

Pack the plums, cloves, star anise, cinnamon, peppercorns and fennel seeds into the jars, leaving 1/2 inch at the top. Ladle the hot brine over the plums, stopping 1/2 inch from the top. Using the tongs, screw the lids and rings on the jars securely but not too tightly.

Step 5

Using canning tongs, lower the jars onto the rack in the boiling water, making sure they are covered by 1 inch of water. Boil over high heat for 20 minutes. Using the canning tongs, transfer the jars to a rack to cool until the lids seal (they will be concave); refrigerate any jars that do not seal. Store the sealed jars in a cool, dark place for up to 6 months.