I understand that. But if it were iron transfer to the apple, then every knife would transfer an iron taste to an apple. Most people seem to jump at sulfur from the smell generated when cutting onions. But this was an apple not an onion. On top of that, I am not aware of sulfur being a compound found in blood, but copper is. Most people who say something has a blood-like taste would also probably say it could be described as a metallic taste. So, back to copper.
I have found apple to give a nice blue patina on white and blue steels, helped with reactivity issues. I now cut some apples whenever I want to start a patina. No experience with W2 here, though.
It's the same with my Aogami 2 Knife. This metallic taste on apples. But just on apples, nothing else. No weird smell with onions, pineapples etc. So far, the patina was no help with this issue.
When I used the Fowler passaround I didn't cut any apples, but I did see browning on white onion. This happened each time I used it and it did have a patina.
"The Buddha resides as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain."
Out of curiosity I just took my Tanaka aoniko petty to an apple, it had no patina before I started. After a few slices, I got black staining on the apple and metallic smell and taste. The blade now has a nice blue patina overall, I will test for reactivity with patina tonight, though it probably needs more time to build up.
My Fowler W2 was also very reactive just like yours. It's very simple to solve though by forcing a patina. All i did is heat the blade under the tap, cover the blade with beef blood, leave for ten minutes, and i was left with a blade that is almost stainless in terms of food reaction.
On a side note, I used my Ealy on some hot Italian sausage and it got a nice rainbow-blueish patina. I left the fatty meat residue clinging to the blade for a while before rinsing.
"In Japan they don't call it Japanese food, they just call it food." -- Children's Hospital Quote