Plum Jam

This is our very favorite jam, just like my mom made years ago. The recipe is from the “1972 Ball Blue Book”, modified to current guidelines. In 1972, I didn’t water-bath this jam; I used paraffin to seal the jars. Water-bath processing is a much surer way to save this delicious jam. Check this link for the basics.  
I do have to buy plums in season; I haven’t found a good source of tart plums like we had when I was a kid. Red Santa Rosa plums are a good choice.  This recipe doesn't call for pectin, so it is a little cheaper to make.  
I often sit on our patio while I pit and cut up the plums.  I try to make 3 or 4 batches of this jam every summer - it goes fast.

Plum Jam
4 pounds Plums -- red tart ones
6 cups Sugar -- 2# 12 ounces
1 1/2 cups Water
1/4 cup Bottled Lemon Juice
Pit and slice plums into 6ths or 8ths, then cut in half. Measure 2 quarts full.  Place multiple shallow sauce dishes in freezer to use to check jellying.  Sterilize your jars in the water you're heating in your canner (about 8 half pints).
Combine all ingredients in open kettle; bring slowly to boiling, stirring occasionally until sugar dissolves. Cook rapidly almost to jellying point, about 25 - 30 minutes, stirring frequently to prevent sticking - about 215-216 °.   If  jelly wrinkles when you push it with your finger in your cold dish it is ready.
Pour, boiling hot, into hot jars, leaving 1/4" headspace. Wipe rims and adjust prepared lids.  Process 7-10 minutes in boiling water bath. Set on clean towels to cool.
Equipment: Open kettle, boiling water bath canner with rack, 2 quart measure, large metal spoon for skimming foam, instant read thermometer, large silicone scraper or spoon, jar lifter, lid wand, tongs for jars, funnel, ladle, ruler, pan with paper towels for filling jars, clean towels.
Cost August 2019: $4.99 or 63¢ per 8 ounce jar. (plums at 88¢ per pound and sugar at $3.99 per 10 pounds) - an 18 oz jar of the cheapest plum jam was $2.49 at Fareway, 18 ounces of this recipe equals $1.40. Commercial jam contains high fructose corn syrup and corn syrup. I usually buy cane sugar.
Do not double batches. Use the large open kettle to cook down rapidly and keep splashing to a minimum.  Read directions with your lids to prepare them.
Yield: "8 Half Pints"