Prepare boiling water canner and sterilize 5 12-ounce jars by boiling them for ten minutes.

Wash lids and rings and bring to a simmer in a separate, small saucepan of water.

Turn off heat and allow jars, lids, and rings to sit in hot water until needed.

In a heavy-bottomed, non-reactive pot, bring plums, water, onion, garlic, ginger, and chili peppers to a boil and then reduce to a simmer.

Add sugar, vinegar, spices, and soy sauce to the plum mixture and continue to simmer until plums are falling apart and the mixture is quite soft, about 20 minutes.

Remove cinnamon stick.

Pass mixture through a food mill in batches into another non-reactive saucepan.

Return the mixture to a boil, reduce to a simmer, and cook until the texture is pulpy and saucy.

Remove from heat.

Ladle into prepared jars, leaving a half inch of headspace.

Wipe the rims of the jar lids with a clean kitchen or paper towel and seal.

Place the sealed jars back into the canning kettle, ensuring the water level clears the jar lids by at least one inch.

Bring the water back up to a boil over high heat. Once boiling, set a timer for ten minutes.

After ten minutes, turn off heat and allow jars to sit in water for five additional minutes.

Using a jar lifter, remove the jars to a cooling rack.

Once jars have reached room temperature, remove rings and test that all lids have sealed properly. Store unsealed jars in the refrigerator.

Label and store sealed jars in a cool place out of direct sunlight.