Why does the water turn green when cooking jerusalem artichokes?

Factual Questions
1

I steamed jerusalem artichokes (sunchokes) in a stainless steel steamer, and the water in the bottom was a lovely emerald green afterwards! A quick google showed this happening to others, but no explanation as to why. Any takers?

2

Chlorophyll

3

But lots of other vegetables contain chlorophyll, and yet they don’t turn cooking water green.

4

Jerusalem Artichokes don’t contain chlorophyll.

If they’re the purple-skinned variety, then the pigment in the skins is probably due to anthocyanins (as also found in red cabbage, blueberries, etc) - and this will react with alkaline water (such as tapwater in a hard water zone) to produce a lurid blue colour.

5

Some do. I’m fairly sure I’ve seen spinach and broccoli tint water green.

6

I think there might be some conflation abroad in this thread.

Jerusalem Artichokes are the tuberous roots of a species of sunflower, Helianthus tuberosus - and they look like this or this. Under normal circumstances, they do not contain chlorophyll, because they grow underground.

Globe Artichokes do contain chlorophyll, because they are the scaly flower buds of a type of thistle, Cynara cardunculus var. scolymus - and they look like this, but they are not the topic of this thread.

7

The ones I used were beige-skinned, but I peeled them first anyway. So they were peeled, sitting inside a stainless steel steamer that had no direct contact with the boiling water, yet the water was a bright emerald green afterwards.

Obviously some kind of reaction, but what?

8

It looks like there’s a family of compounds called leucocyanidins that are related to/precursors of the anthocyanin pigments, but are colourless - seems these are present in plants of the genus Helianthus and are responsible for discoloration after peeling (peeled jerusalem artichokes turn brown-black on exposure to air), so I suggest it’s something to do with this - probably in conjunction with the metals of the pan, and dissolved minerals in the water (obviously not in the steam - which will be more or less pure water, but in the boiling liquid when the juices drip down).