This jam turned out beautifully: Deep rich color and tangy, sweet, and deep flavor.
Now, making this jam takes two days. The work is minimal on the first day, but you should know and plan accordingly.
This is the base recipe. You can make up to three times as much (which I did by accident), but note that cooking time will be longer for bigger batches. Just multiply the following recipe by two or three, and you are good to go. Three kilos of cleaned plums yielded 11 eight-ounce jars of jam.
Here's what you will need:
- 1 kilo of quartered plums with the stones removed (in other words, you need a little more than a kilo of plums)
- 700 ml of white granulated sugar (I prefer to use organic, which has just the slightest scent of raw cane--mm, lovely)
- juice from one lemon, strained (if you don't have lemons, I suspect that about 100 ml of balsamic vinegar would yield an utterly amazing jam)
- 2-3 sprigs of fresh rosemary
- clean jars (sterilized if you are not planning to eat this right away, but more on that later)
Day 1
Prepare your plums. Cut them into quarters and remove the pits. You don't have to peel them; the peel is where the jam will get its pectin from.
I love this color combination.
When you have about 1 kilo of cut fruit, add the sugar in layers. Start and end with a layer of sugar so that the fruit is completely surrounded with the sugar. Also add the lemon juice.
Then put your fruit-sugar-lemon juice combination into the refrigerator for one day. The reason for this is to draw the juice out of the plums and start to break down the cell walls. (You can let this sit for up to two days without any problems. Longer than that and your jam may start to get a little raisin-like.)
Day 2
Today you will do most of the work. Start with washing your jars and lids and sterilizing them. You can do this in a water bath, but I like the oven technique that I learned from Rachel Saunders's book The Blue Chair Jam Cookbook, although I upped the heat a bit.
To do this, place your washed jars and lids on a cookie sheet and place them in the oven. Turn on the oven (I prefer to place the jars into a cold oven so I don't risk cracking them with a big shock of heat) and let the temperature come up to 275 degrees Fahrenheit (that's 135 degrees Celsius for my international friends). When the oven is hot, the jars should remain in the oven for at least 30 minutes. Leave the jars in the oven until you need them.
Next, put a plate with five metal spoons in the freezer. Now, pirouette and sing Oye Como Va. Ha ha! I just wanted to see if you were still paying attention. You don't have to sing and dance, but do put the spoons in the freezer, you will use them to test the doneness of your jam.
When you made your preparations, you can start heating up your fruit mixture, which should be a lot more watery than it was when you first put it in the refrigerator. Start with medium-low heat and bring the temperature up slowly.
Once the mixture has started to simmer a bit, raise the heat to medium-high. Get a good boil going (the point is to let most of the water steam off and candy the sugar). Stir frequently (wear something to protect your hands; the jam will sputter a lot and it can burn you). When the mixture foams, skim off as much of the foam as possible. (Use a skimmer for this job; it really makes a difference. Also, keep your skimmer in a bowl of cold water, which will help the foam adhere to the skimmer.) You will skim very frequently for the first 5 to 10 minutes.
Let it boil for about 20 minutes before you do your first doneness test (add about 10 minutes if you do a bigger batch). To do the test, remove a small representative sample from the pot (in other words, get both solids and liquid) and transfer it to one of the frozen spoons. Place the spoon back in the freezer for 3-4 minutes. Feel the bottom of the spoon, if it doesn't feel cold or hot, you can inspect the jam. The liquid part of the jam should move a little, but it should not run. If it runs, the jam is not ready yet. Keep cooking the jam for about 5-10 minutes and test again.
When the jam is done, take it off the heat and add your sprigs of rosemary (if you don't want to use rosemary, skip this step). Let them steep for about 5 minutes and then remove them. (You don't want slimy rosemary sprigs in your final product.)
Take your cookie sheet with jars out of the oven and fill the jars. Using a jam funnel is helpful for keeping things somewhat clean. Be very careful, the jam will be extremely hot.
Don't completely fill the jars. Leave at least one quarter inch at the top. Clean the rims of the jars with a clean wet cloth (or paper towels, as long they aren't prone to tearing). Then place the lids on the jars and loosely screw on the rings. Put the jars back in the oven for 20 minutes.
When you remove the jars from the oven, put them somewhere you will not disturb them for about a day. That will give the jam time to set and create the vacuum seal. Next day, check the seals. The bubble in the middle of the lid should be depressed. If it makes a popping sound when you press it with your finger, you didn't get a vacuum seal, which means you should use that jar right away. Just put it in the refrigerator and eat it within two weeks. The rest of the jars can go into a cool, dark place for enjoyment later in the winter. Yum!
If you want to learn more about jams and other preservation techniques, check out the National Center for Home Food Preservation.