My neighbor has a Mexican plum tree loaded with plums. Do any of you have a good recipe and instructions for making Mexican Plum jam or preserves?

I used to help my Mom make sand plum preserves, but that was in the 60's so I need a refresher. Mom is 94 and is coming to help, but I want to make sure I have everything on hand before she gets here.

What is the usual yield from the plums after they are processed? For example, if we want to make a gallon of preserves about how many plums would it take?

my mother used to make all sorts of jellies and jams, while she was still alive, I went to her house to intentionally learn all her tricks and took notes along the way. below is the recipe I captured from that wonderful afternoon I spent with her.
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1 qt. Plums
1 qt. water.
5 1/2 cup juice from cooked plums
7 1/2 cup sugar
1 pkg pectin (sure jell)
1T butter

Remove seeds and cover with water and low Boil plums till skin falls off fruit.

Strain juice to remove skin & meat of plum and save meaty portions for jam if desired.

Put juice in dutch oven over medium to high heat, stir in pectin & butter and bring to full boil, while stirring constantly.

Add sugar and return to rolling boil. Rolling boil for exactly 1 minute. (note 1 minute on the dot, not 59 seconds and not a minute & 1 second, this is the key)

Remove from heat, skim foam and put in clean jars while hot. Put lids on to seal and let cool.
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my wife and I have used this multiple times over the years with great success using plums, wild plums, mustang grapes, peaches, etc.

Perfect, that's exactly what we needed! That is awesome that you got to spend that time with your Mom and document her recipes.

A few questions:

Is the "5 1/2 cup juice" from plums cooked separately, and then added to the 1 quart of plums?

Do you ever vary the amount of sugar depending on the sweetness the fruit?

After the lid is on, do they seal themselves as they cool? (My Mom used to melt wax to cover the preserves. I'm not sure if that was needed).

My Dad loved sand plum preserves, so it was an annual tradition to keep an eye on the bushes and get them when they were ripe.

the 5-1/2 cup juice is the by product of the cooked plums with meat & skin removed ... that's the liquid you start with to make the jelly. You can remove just the skins, leaving the meat of the fruit if you want to make jam ... same thing, 5-1/2 cup juice & meat to start with.

no, never varied the sugar quantity ... use the same amount regardless of what fruit or sweetness/bitterness

if you put the final product in the jar still warm/hot, the lids will self-seal ... both my grandmothers put wax / paraffin over the top before putting on the lids, but my mother never did. As long as you get a good seal on the lid, you should be fine.

my wife & I do this same recipe with peaches but after cooking it down, remove the skins and run the juice/meat mixture thru a blender to puree, then start the the rest of the process, comes out great ...

Got it, I was reading it like an ingredients list at first!

That is what I thought on the wax seal. I found an article that talked about the old wax seals coming from the days of open crocks when the lids alone weren't able to provide the seal.

I'll give it a try with our plums and see how it comes out. Thanks!