Less costly

For instance, a middle-sized Chongqing hotpot restaurant may normally consume 20,000 yuan worth of oil a month, and obviously the restaurant has strong incentives to cut costs.

Large, more reputable restaurants may consider other factors.

One veteran cook interviewed by China Newsweek recently said a large restaurant might choose not to use swill oil, because it heats slowly, and usually turns blackish after being used a couple of times.

Crudely processed swill oil looks like cola, and gives off a bad smell. But once purified with calcium bicarbonate and neutralized with alkali, the oil begins to glisten like tea water, and is virtually indistinguishable from good oil to the naked eye - or detecting devices.

Only two of the 10 samples made of the swill oil found in the Ningbo crackdown appeared to be substandard when tested. So some restaurateurs may plausibly plead ignorance even after they have used the swill oil, especially when swill oil is added to good oil.

There are many complaints against food security watchdogs that fail to intervene earlier, and technological supervision departments that fail to function even when confronted with swill oil, but rarely, if ever, against residents and consumers, who are often perceived as "victims" rather than as miscreants chiefly responsible for wasting a stupendous amount of food in the first place.

Wasteful habits

As a result, the ultimate solution to the swill oil problem lies with ordinary residents, who prefer to have their dishes prepared with liberal use of oil. In a Chinese restaurant, wastefulness and extravagance are still interpreted as evidence of generosity.

The liberal use of oil in cooking is unnecessary from a health point of view. Today, with the specter of swill oil hovering near, that habit of eating rich, oil food takes on additional health risks.

According to statistics from Beijing, the amount of edible oil consumed in the city in 2009 totaled 600,000 tons, of which 15 percent ended up in the gutter - meaning a potential 90,000 tons of swill oil. About 25,000 tons of that oil were scooped from restaurant drains, and then sold to unlicensed private processors, because the "black" swill processors pay better and provide better services than the licensed collectors.

There are also implications for policy makers. Gutter oil, 98 percent-biodegradable, can be a clean alternative to diesel processed from petroleum.

German and Japanese governments reportedly collect gutter oil at subsidized prices and then turn it into fuel.

In the United States and South Korea there are also legal incentives for the use of biofuel.

But in China, legal gutter oil processing plants are being edged out of the market because they cannot pay as much as illegal gutter oil collectors.

It is reported that in Shanghai there are only 23 legal collectors, and in Beijing, only four. Naturally they could handle only a fraction of the gutter oil produced.

This year the Chinese government has offered tax breaks to help make biofuel from gutter oil, but it remains unclear how the subsidy could directly benefit the biofuel makers.