It’s got quite a history! I’m remembering it used to be a drink made with alcohol, maybe in Turkey! ETA Maybe that was sylabub…
I can’t find the post (and can’t share the whole CI article) but I remember trying to figure out if various citrus juices have the righ pH to set.
Here it is!
The CI piece says “Because a properly set posset needs a strong acid, you don’t often see it prepared with anything other than lemon juice …”
and
"test batches of grapefruit (pH 3.1), orange (pH 3.6), and pineapple (pH 3.9) confirmed that these variations would not set without the help of citric acid.
Hopefully I haven’t copied too much. I’ll ask the mods.