Fill water bath canner 3/4 full with water. Turn stove top on high
While waiting for canner to boil, wash plums and remove stems
Place lids and rings in boiling pot of water to sanitize, then turn off and let sit until you are ready to use them.
Wash jars thoroughly. Once the canner water begins to boil, place jars 3 at a time into the canner on their sides so the water can get inside them. Leave to sanitize a couple of minutes, then pull them out with the jar lifter and set on a dish towel.
Once the jars are sanitized, you can begin filling them with the plums. 10-12 plums should fit in each jar. Leave 1 inch space from the top of the jar. Do not press them down as this could squish them.
Add the water, sugar and spices (if using) to a pot and bring to a boil. Once boiling, turn off the stove top and pour the hot brine into the jars. Be sure to leave 1 inch space from the top of the jar.
Wipe the tops of the jars and around the threads with a clean, damp cloth. Put the lids on and tighten the rings.
Set the filled jars into the water bath canner and bring it back to a boil. You might need to add more water to be sure the tops of the jars are covered by 1 inch of water. Once the water is boiling again, set the timer for 20min. After 20min. , pull the jars out of the canner with the jar lifter and set on a dish towel on the counter, not allowing the jars to touch.
Let cool. Once the jars are cool, check that the lids have sealed by pressing down on each lid. If the center of the lid pops back up, it did not seal and you will need to put that jar in the refrigerator.