Recipe yields 9 pint jars.

PREPARE FOR CANNING

• Wash the jars you'll use, making sure each is clean and free of nicks in the rim, which could impede sealing.
• Wash the lids and rings in hot soapy water. (If you're using non-Ball brand lids, prepare as suggested by manufacturer.)
• Place empty jars in a canning pot or large stock pot with enough water to cover by an inch or two, cover pot, and set on high heat. It can take awhile for the water to heat, so get it started before you begin making the recipe.

PREPPING THE SYRUP AND PLUMS

• Combine sugar and water in a large pot; bring to a boil. 
  1 cup sugar, 6 ½ cups water
• Meanwhile, prepare plums. For halves, remove stems and cut each plum in half; discard pit. To can whole plums, use a fork to puncture the skin on opposite sides of the fruit.
  9 pounds fresh plums
• Remove jars from the canner, draining the water back into the pot. Raw pack: Pack raw plums into jars snugly. Cover with hot syrup to a 1/2" headspace. Hot pack: Place whole or halved plums into the hot syrup and boil for 2 minutes. Turn off the heat, cover the pot, and let stand for 20-30 minutes. Use a slotted spoon to transfer plums into jars. Pour hot syrup over plums, leaving a ½ inch headspace.
• Run a non-metallic knife or chopstick around the inside of the jar to release air bubbles. Add more syrup to maintain the ½ inch headspace if necessary.
• Wipe jar rims to remove any residue that may have spilled. A clean rim is essential to a good seal.
• Set jar lids in place. Screw bands on finger tight.

CANNING

• Use a jar lifter to gently submerge jars into hot water in the canning pot. Water should cover the top of the jars by one-to-two inches. The water will cool somewhat in reaction to the addition of the jars. Return the water to a simmer and then set the timer.
• Process pints for 20 minutes, quarts for 25 minutes at 0-1,000' feet altitude; 25/30 minutes (pints/quarts) for elevations between 1,001-3,000'; 30/35 minutes (pints/quarts) for elevations between 3,001-6,000'; or 35/40 minutes (pints/quarts) over 6,000'.
• Remove jars from water using the jar lifter and transfer to a solid, towel-covered surface. Allow to cool for 24 hours.
• Check seals. Lids should be solid and pulled down tight. (if they flex and pop, the jar didn’t seal; put unsealed jars in the refrigerator and use those first).
• Remove rings and wash outsides of jars. Store in a cool, dry place.