I've never bought the official explanation for this. We have just four iron atoms per hemoglobin. But the roughly quarter-billion of these per red blood cell are in the red blood cells, which presumably haven't all suddenly lysed and dumped their hemoglobin.
I think we should test with blood plasma first. I'm thinking it is the various salts in the plasma we're tasting, not the iron bound up in hemoglobin which is itself trapped inside of red blood cells.
