Wash plums thoroughly, cut them in half and remove the bone. Put them in a saucepan with the sugar and lemon juice and let stand for 1 hour.
After this time, heat over medium heat and let the preparation cook for 40 minutes, stirring occasionally. When the jam is reached, remove from the heat and, if desired a finer texture, crush with the blender or passeras.
Pour the jam gradually into pre-sterilized glass jars and close them tightly.
To make the vacuum, place a cloth at the bottom of a casserole, place the jars on top, and cover with water. Bring the water to the boil and leave it for 30 minutes from boiling. Let the jars cool, dry them well and don’t forget to label them indicating which product it is and the date of manufacture.
How to sterilize glass jars. Before filling them with jam, they should be sterilized to avoid contamination. To do this, they should be placed in a pot of boiling water for 10-15 minutes. Afterwards, they will drain and dry well, trying not to touch the inside of the jars.