Select firm plums that hold up well during canning—soft, mushy varieties don’t do as well. You’ll need about 9 pounds of plums for a full batch.

Rinse plums gently under warm water, using your fingers to rub off any dirt. Inspect each fruit for bruises or soft spots, setting aside any that are damaged.

Check your canning jars for any cracks or nicks that could cause problems during sealing. Holding each jar up to light helps spot any flaws.

Wash the jars thoroughly and place them in your water canner. Fill with water and bring it to a boil. Keep the jars hot until you're ready to fill them. In a separate saucepan, simmer the jar lids on low heat to soften the adhesive.

Combine 6 ½ cups of water with ¾ cup of sugar in a saucepan. Stir, then bring it to a boil over medium heat for about 1-2 minutes. This light syrup balances the tartness of the plums. If you prefer to skip the sugar, you can can the plums in just boiling water for a lower-calorie option.

Use a sharp knife to prick each plum several times on the sides. This prevents the plums from splitting as they cook. If desired, you can halve the plums and remove the pits, but whole plums hold up better in the canner.

Using a jar lifter, remove the hot jars from the canner. Pack each jar tightly with plums. Narrow-mouth jars are best for this, as they hold the fruit in place better than wide-mouth jars. Fill each jar with the prepared syrup, leaving ½ inch of headspace.

Run a knife along the edges of the jars to release any air bubbles. Wipe the rims of each jar with a damp paper towel to remove any sticky syrup that might prevent the lid from sealing properly.

Place the filled jars into the water canner. Ensure that the lids are covered by at least an inch of water. Bring the water to a rolling boil, cover the canner, and process for 20 minutes. If you’re at higher elevations, adjust processing time accordingly.

Once the processing time is up, turn off the heat and remove the canner lid. Leave the jars in the canner for 5 minutes to stabilize the pressure. Using a jar lifter, remove the jars and place them on a towel or cutting board to cool.

After 24 hours, press down in the center of each lid. If it doesn’t pop or click, the jar is sealed. If any jars didn’t seal, refrigerate them and use them within a couple of days.

Once sealed, remove the rings and label each jar with the date. Store the jars in a cool, dark, and dry place. Your plums will be shelf-stable for up to a year, although you’ll probably eat them long before that!