Here's a before and after picture to illustrate just how much the peaches dissolve and caramelize:
The blogger I got this recipe from states that the jam will keep on a shelf for a year. Note this is without boiling the jar through the canning process. I just went ahead and put mine in the fridge. I guess to be safe multiple jars could be canned or frozen.
Peach jam (Marmellata di pesche)
Adapted from Il cucchiaio d‘argento (The silver spoon) via Rachel Eats
Smaller quantity : yield 3 – 4 jars
2 lb 10 oz ripe peaches
2 1/4 cups sugar
Larger quantity : yield 5 – 7 jars
4 1/2 Ib Ripe peaches
3 1/2 cups sugar
Peel the peaches (as you would tomatoes) by putting them in a large bowl and covering them with boiling water. After a minute, using a slotted spoon. scoop the peaches out of the boiling water and lower them into another bowl of cold water. After 30 seconds scoop the peaches out of the cold water and working quickly with your hands or a sharp knife, skin the peaches.
Cut the skinned peaches in half, pull away the stone and then slice each half thinly and place in a large, heavy based saucepan. If the peaches are very ripe and juicy, it is not necessary to add extra water, otherwise add 5 tablespoons. Cook the peaches over a low flame until they start to become mushy, the add the sugar and stir until it has dissolved. Bring the jam to the boil, then reduce the heat and cook the jam over a low flame, stirring occasionally for about 2 1/2 hours. The jam will reduce significantly, darken and caramelize, it should be dense, coating the back of your wooden spoon.
Ladle the jam into warm, clean (sterilized) jars and then seal tightly while they are still hot, label once they are cool and store in a cool dry place.