Plum jam without addition of gelling agent

From the garden of my good friends in Horsens I have receive a portion of fresh plums, which I have turned into some jam using my jam recipe book as inspiration with a few modifications.

As I could not figure out, why some of the plum stones should be cracked and added into the cooking pan, I decided not to do to, so people eating the jam would hurt some of their teeth.

The texture of the final jam is a little to the slimy/ropy side, which I have no explanation to, why it is so.

Plum jam: - 4 glasses

• 700 g plums - washed, de-stoned and cut into half
• 225 ml water
• 700 g sugar

1. Prepare the plum by washing, de-stone and cut into half. Place the plum pieces into the cooking pan and pour the water in as well.
2. Put the cooking pan on the stove, heat up the content, so the plums are simmering. 
3. Let the apple simmer until the plums become pulpy in texture, it takes between approx 20-30 minutes.
4. Prepare the jam glasses either by heating up in the oven or adding boiling water to them.
5. Add the sugar to the plum mass and stir until it is dissolved.
6. Bring the jam to a rolling boil and boil hard until the setting point is reached. Stir the jam frequently.
7. Test of set after 5 minutes using the flake test.
8. When the setting point is reached, remove the pan from the heat and leave it to stand for approx.  5 minutes. As the jam settles, push any scums from the surface of the pan to the side and remove it with a metal spoon. The purpose for the waiting step is well to build viscosity in jam, so the fruit pieces will be trapped inside the jam inside of be going to the top of jam.
9. Gently stir the jam after the resting time and pour it into the prepared glasses, fill the glasses up to the brim. Remove any scum for the surface of the jam using a tea spoon. Close the glass with a lid.
10. Leave the glass upright and disturbed to cool and set.
11. Store at ambient temperature.