Making Plum Jam

Yellow plum jam is the latest product, as well as some lemon balm jelly – an experiment that needs work. A nice little stock of jars is starting to mound up, although nothing to the 58+ pints put up so far by our friends at Well Preserved.

I don't consider myself a plum expert yet, so I'm not posting instructions. They're a little fussy because you have to take out the pits. I have tried the old-fashioned technique of cracking open some of the pits and using the pith to flavour the jam, but it's incredibly fiddly to open them, and anyway I have the impression that the pleasant bitter almond scent indicates cyanide content – or has all my murder-mystery reading steered me wrong?

While on the subject of chemistry, it seems to me that there's a correlation between high pectin content and a change in the colour of a greenish or yellowish fruit like gooseberries or yellow plums to a pinkish red. If I recall correctly, I think it's quince that's supposed to develop a ruby red colour; it's also high in its own pectin. I actually looked it up yesterday but couldn't spot anything on the science of it; anybody know?