Plum Preserves

The art of making fruit perserves has been in my family for at least several generations now.  My personal favorite is blackberry (my parents' house has a ton of bushes).  In college I took up the family heritage of jam making and to date I have made strawberry, blackberry, guava (jelly), and now plum.  My reason for trying plum was one of economics; blackberries are expensive in suburban Sacramento and our friends Melody and Luke have overly-productive plum trees in their backyard.  Last weekend was their annual plum harvest, and we gladly took about 15 lbs. home.  These preserves came from 4 lbs of that.

The recipe I followed comes from the Sure*Jell pectin.  MPC has a different recipe that I will have to try and compare.  I will post those results when I have them.  Until then:

Ingredients:

6 C cooked plums (exact)

8 C sugar (exact)

1 packet (1.75 oz/49g) fruit pectin [gelling agent]

1 squirt lemon juice (not exact) [acid]

The entire process from raw fruit to preserves took a little over an hour

Step 0: sterilize the equipment:

As a microbiologist, I have learned that bacteria and other microbes lurk everywhere.  To prevent contamination you must sterile the jars and lids.  Since most of us do not have access to an autoclave, putting the jars in the dishwasher works fine (it is hotter and longer, therefore more sterilizing, than hand-washing).  Do not put the lids in the dishwasher, this will destroy the vital seal on the lids.  Instead once the plums are cooked (step 1 & 2) fill a bowl with boiling water and place the lids inside, making sure lids do not stick together.  Make sure lids are completely submerged.

Step 1: how does one cook plums?

wash, pit, and chop up plums (do not peel!!).  Using the kitchen scale I found that 1 plum averages to just over 1 oz weight.  You need 48 oz (16oz/lbs * 4lbs) so get started.  This is by far the most time consuming step.

4 pounds of pitted plums ready to chop

Step 2: Actually cook the plums:

In a saucepan  add 1/2 C water and 4 lbs. chopped plums.  Bring to boil, cover and reduce heat, and simmer for 5 mins.

6 cups cooked plums

Step 3: Now to make jam! (reminder, now place jar lids in bowl of boiled water)

This part is fun.  As you may have noticed jam is basically fruit, sugar, pectin, and maybe lemon juice.  The ratios differ depending on the type of fruit.

For a proper preserve to setup, which differentiates this fruity mixture from a sauce, compote, etc., we need the sugar and pectin to interact appropriately in an acidic environment.  Fruit naturally contains both acid and pectin, but may not have enough of either for the gelling process to occur.  To insure success additional pectin and acid (lemon juice) may be added.  Certain low-acid fruits require a significant addition of acid (1/4 C depending on fruit)

To start pour 6 cups cooked plums into a 6- or 8-quart saucepot.  At this point I added a squirt of lemon juice.

Lemon juice as insurance

Measure 8 cups of sugar into a separate container and set aside.

Stir pectin into the fruit mixture (an optional tablespoon of butter can be added to help prevent excess foaming)

Next on high heat bring the pot to a "full rolling boil" (sure*jell describes a "full rolling boil" as "a boil that doesn't stop bubbling when stirred".  Be sure to keep stirring constantly. 

Stirring constantly

Once at a rolling boil, add the sugar and quickly stir in.  Return the mixture to a "full rolling boil" and boil for exactly 1 minute. (from my understanding once all the ingredients are added and it begins to boil you have reached "the point of no return", meaning the chemical reaction between sugar and pectin has started and can't be stopped.  So simply make sure you now finish the process.

After boiling for exactly 1 minute swiftly ladle this napalm into your sterile jars (be sure to have paper towels or something underneath the jars, this can get messy).  

Fill jars within 1/8 inch of the lid trying not to pour jam onto the jar rim.  

ladle the napalm into jars

Once jars are filled use a damp paper towel to quickly wipe off the jar rims (otherwise this will prevent a proper vacuum from forming in the jars.

After rims are clear place lids on the jars, and use lid rings to secure.

Now wait and allow jam to cool.  

As the jam cools it will condense and create a vacuum with the lid (this is how you know the jar is sealed).  

When a vacuum is formed the lids will "pop" down (appearing concave instead of convex.)  Within a few minutes to an hour + you should hear the lids pop.  
Wait several hours and check to see which lids have popped and which have not.


Those lids which popped are now good to go, and can sit on your pantry shelf for quite a while.  Any jars that did not pop are still good, but need to be stored in the refrigerator.  Any partially filled jar will also need to go into the refrigerator.


If an unopened jar's lid ever pops on its own discard it.  This indicates the presence of microbes producing gases that have canceled out the vacuum.  But as long as the vacuum remains (as indicated from a "popped" lid nothing is growing inside.


I say this as a theoretical warning, I have never had a jar go bad on me, but better safe than botulism.


Enjoy, and welcome to the jam-makers club.