When I worked at the Foodland in Elizabeth, there was a Greek lunch counter across the street; I was there at least twice a day. I don’t normally pay that much attention to how things are cooked, but the tub, or container, or whatever you call it, of hot oil for French fries was directly across from my usual seat, and I noticed the oil got a little darker each day, then started over fresh on Fridays.
They used that fresh Friday oil all week, that’s why it kept getting darker. After a week, they used it to cook their Friday fish special. When I told my wife about this, she said “That’s disgusting.” I couldn’t say, I never ordered the fish special.