This video, produced by Radio Free Asia, shows in excruciating detail how a couple of gutter oil vendors go about their work. It starts with the couple scooping sewage out of the ground, and it ends with unwitting Chinese consumers chowing down on the end product:
To reiterate, this is illegal, something that Chinese authorities are trying to stop and not used by all street vendors. But it's also thought to be widespread. Being reprocessed garbage and sewage, gutter oil contains all sorts of untold carcinogens. Many of the operations, like the one shown in the video, are small-time. But there's enough money to be made that some producers go much bigger.
In April, Chinese authorities uncovered a gutter oil production ring that spanned 13 cities and over 100 people, who somehow acquired rotten animal parts and boiled down the fat into oil. The sting, which came after a five-month investigation, yielded 3,200 tons of the stuff; authorities estimated the black-market producers had already sold a stunning $1.6 million worth of their product.
Don't cancel any vacation plans to China over this. Food in China is delicious, and gutter oil typically is used just in some street food stalls or cheap, hole-in-the-wall dives. But it is a reminder why authorities there are deeply concerned about food safety issues.