It turns out that for cooking, which the Chinese brisk trade on the streets, often used the so-called "sewage oil". This fat collected from such, to put it mildly, unappetizing sources, such as sewers, grease, slaughterhouse and so on. All this fat is processed and passed off as conventional oil.
What you see below - a screenshot video taken resident Chinese city of Shenzhen. It toiler of the food industry produces manhole oily muck, which then will be fried food.
But first, this swill go for processing in a special underground facility, where it will connect with other animal fats, filter and boil.
In the end, revised in such a way "oil" gets to the street vendors and owners of cafes in the open air.
Here is the video in full: