What to Never Eat at Fast Food Places, According to Fast Food Workers [Health] - http://pulse.me/s/b6PQ
When I was a young buck, I worked at Burger King. Here is how the oil rotation went. You had four vats of oil that you cooked fries in. And boy did you cook fries. Tons of them. After about 2 days worth, the oil got too dark for fries. So we switched it over to the ones for chicken. Since it was darker, it was ok. Then that goes on for a week. After a week of massive frying. The oil is black as motor oil. At that point, it's switched to the Fish Filet vat. That's the only thing you cook in that vat.