I think that the protiens in the powdered milk are why it tightens the scales on the herring, resulting in the shine and tougher skin. I use a combo of tap water, powdered milk, kosher salt(to leach moisture), sugar to harden, and borax so I can do 10 dozen at a time and they keep for a few weeks, but 10 doz usually lasts me about 5-7 days depending on how hard and selectively I fish-T