Every boy or girl brought up in the countryside will have experienced this. And every maker of jam will know all about scum.
When your Mother (or Father) made her (or his) Raspberry or Strawberry Jam, they would always skim off a certain amount of 'scum' from the boiling jam, and place it in a small bowl, or on a saucer.
For the children of the house this was a real treat. A thick slice of fresh bread liberally spread with butter, and a good dollop of warm scum, was heaven on a plate. It was the Jam makers audience's treat.
I asked Lady Magnon recently if she'd like some scum. After rolling her eyes, and looking at me with suspicion, I explained what it was and she eventually tried some.
Her verdict? She loved it, after all it's just freshly made jam without the pips; although mine had some actual jam it in, leftover from the filled jars.