If preparing with sweet plums or freestone prune plums, use 3-1/2 cups prepared juice and add 1/4 cup fresh lemon juice.
How to Measure Precisely
To get exact level cup measures of sugar, spoon sugar into dry metal or plastic measuring cups, then level by scraping excess sugar from top of cup with a straight-edged knife.
At altitudes above 1,000 feet, increase processing time as indicated: 1,001 to 3,000 feet - increase processing time by 5 min.; 3,001 to 6,000 feet - increase processing time by 10 min.; 6,001 to 8,000 feet - increase processing time by 15 min.; 8,001 to 10,000 feet - increase processing time by 20 min.
Jam or Jelly Didn't Set?
Every once in a while, you may find that your jam does not set the way you expected. If your efforts resulted in a runny batch, try our Remake Directions to improve your finished jam. If your jam still doesn't set, you can always use it as a glaze or syrup.