L-Cysteine (E920): Feather-Derived or Vegan?

L-cysteine's status is entirely a sourcing question. It has historically been produced from keratin sources — duck feathers, hog hair and, in the past, human hair — but fermentation-produced and synthetic L-cysteine are now widely available. The finished label will not tell you which one is in the dough; the supplier's origin statement will, which is why a review requests it in writing.