Instructions:

Prepare the Plums:

o Wash the plums, remove the pits, and chop them into small pieces.

o Place the chopped plums in a large bowl and crush them slightly using a potato masher or a fork to release some juice. You should end up with about 4 cups of crushed plums.

Sterilize Jars:

o Wash the jars, lids, and rings in hot, soapy water. Rinse well.

o Place the jars in a boiling water canner filled with water and bring to a boil. Boil for 10 minutes to sterilize. Keep the jars in the hot water until ready to use.

o Place the lids in a small pot of simmering water (do not boil) until ready to use.

Cook the Jam:

o In a large, heavy-bottomed pot, combine the crushed plums, lemon juice, and pectin. Stir well to combine.

o Bring the mixture to a full rolling boil over high heat, stirring constantly. A rolling boil is a boil that doesn't stop bubbling when stirred.

o Once at a rolling boil, add the sugar all at once. Stir thoroughly to dissolve the sugar.

o Return the mixture to a full rolling boil and boil hard for 1 minute, stirring constantly. If desired, add the butter to reduce foaming.

Test for Doneness:

o To test if the jam is done, place a small amount of the hot jam on a chilled plate and let it sit for a minute. If it wrinkles when pushed with your finger, it’s ready. If not, boil for another minute and test again.

Jar the Jam:

o Remove the pot from the heat and skim off any foam from the surface.

o Carefully ladle the hot jam into the sterilized jars, leaving about 1/4-inch headspace at the top.

o Wipe the rims of the jars with a clean, damp cloth. Place the lids on the jars and screw on the rings until fingertip-tight.

Process the Jars:

o Place the filled jars back in the boiling water canner. Ensure the jars are covered by at least 1 inch of water.

o Bring the water to a full boil and process for 10 minutes (adjusting for altitude if necessary).

o Remove the jars from the canner and place them on a towel or cooling rack. Let them sit undisturbed for 12-24 hours.

Check the Seals:

o After 12-24 hours, check the seals by pressing down on the center of each lid. If it doesn’t pop back, the jar is sealed. If the lid pops back, the jar didn’t seal properly and should be refrigerated and used within a few weeks.

Store the Jam:

o Label the jars with the date and store them in a cool, dark place. Properly sealed jars can be stored for up to a year.