

I have a PhD in mathematics (set theory). It would be pretty tough to explain to a child. Specifically my PhD is in determinacy, which is way easier to explain than most branches of set theory, but you do need a decent understanding of infinity to really get anywhere.
Making jam is not trivial but it I think that makes it rewarding! My dad has made jam and marmalade for as long as I’ve known and it’s always an event. My parents have hundreds of jars (for some reason my dad calls them bottles? Only in a jam context though!) and every so often he cooks up a giant pot of jam with an old-fashioned sugar thermometer, testing the batch on a piece of baking paper, then bottling everything up. He often did it with my sister, who now also makes her own jam.
He labels all the jars, and we’ve opened jars that were… I dunno, a decade old I’m sure, and they were totally fine. So they will definitely keep for a long time!