Curious about something, was married to a lady of German ancestry and once a year she would cook cabbage and drop a penny in it, in spring if I remember correctly, figured it had to had to do with the bodies need for trace amounts of copper. Just wondered if that was the reason or just good luck, she didn’t know why her family did it but a lot of old traditions seem to have practical reasons. Eating of polk in the spring in the mountains also comes to mind.
I don’t know the science. The Irish do the same though, as do us Northerners. Drop a penny in the pot.
It could be for the copper. It could be to remove the sulphur - new cabbage is a bit rank.