I've made a lot of jams in my culinary life, so I don't usually measure...but my formula is pretty simple: fruit (whatever I have that's not the prettiest or freshest anymore) + sugar + liquid (usually wine) + acid (squeeze of lemon juice).
So, today I had some leftover nectarines from our camping trip that were slightly bruised, some leftover wine- yes, that IS possible in my house, despite what all my friends will claim. I added juice from 1 lemon and some sugar. Easy peasy.
I found these instructions from "Leite's Culinaria: Hot Food, Dry Wit" that seem very close to my process. I use less sugar than she does.
•4 pounds fruit,rinsed and cubed
•2 C organic granulated sugar
•1-1/2 C liquid (wine, water, or a mixture of both)
•1 lemon, halved and juiced
1. Sterilize the jars for canning by boiling them and their lids.
2. To make the jam, place the fruit, sugar, liquid, and lemon juice,into a large pot and bring to a boil over medium-high heat. Continue to cook, stirring the jam constantly, for about 15 minutes.
3. Reduce the heat to medium. Hold the jam at a constant simmer, checking frequently to make sure the jam isn’t scorched at the bottom of the pot. After 15 minutes, check to see if your jam has set by running a wooden spoon down the middle of your jam. If the jam leaves a path, it's set. If the liquid runs back to fill the path, cook it a little bit longer.
4. Place the jam in sterilized jars, leaving about a 1/2" gap to the top. Gently tap the bottom of each jar on the counter to release any air bubbles. Using a damp clean towel, wipe the rims of the jars and secure the lids and rings. Process in a water bath for 10-15 minutes. Remove the containers with tongs and let cool on the counter.
You’ll hear the sound of can tops popping shortly—a sign that a secure seal has been made. Pop, pop, pop. Or, you can refrigerate the jar without processing and use it within three weeks. Enjoy!