The principal of a middle school in Guizhou province was suspended after students smashed the school canteen in protest of alleged use of gutter oil, local authorities said on Monday. A crowd of more than 300 students smashed the windows, dinner tables and chairs of the school canteen in the No 4 Middle School of Renhuai city in Guizhou around 11 pm on Dec 15 after a student said he found a barrel of gutter oil in the canteen, according to a press release by the city\'s publicity office. Students continued gathering on campus in protest until city officials and teachers arrived. The crowd dispersed around midnight with officials promising a thorough investigation. Authorities suspended the principal after the incident and the people who contracted out the school canteen were under control by the local authority. Chen Lianzhong, an official at the news office of the publicity bureau in Renhuai city, told China Daily that tests by the local health authority have not yet determined whether the oil was gutter oil. \"Test results are showing that the oil is no different from normal cooking oil,\" Chen said. \"But lack of a national standard of testing gutter oil is making the identification work more difficult.\" Chen added that oil samples in the school canteen and the source of the oil, a local food and cooking oil shop, have all been tested. Located in the Luban township in the south of Renhuai city, the No 4 Middle School currently has more than 3,000 students and 187 faculty members. Gutter oil, or illegally recycled cooking oil, is often scooped up from sewage drains and gutters behind cooking establishments and then sold to small restaurants. The use of the oil in restaurants has long topped the concerns of Chinese with a large number of reports of illegal production and usage every year. Even so, an accurate scientific method to identify \"gutter oil\" has yet to be found. On Dec 13, the Ministry of Health said on its website that it is still seeking advice from the public for ways to identify gutter oil as current methods are not accurate enough.