Three men who worked at Jinqiao Dairy Company in Northern China’s Shaanxi Province were arrested Tuesday for selling more than five tons of melamine-contaminated milk powder in September, according to China’s official news agency, Xinhua News.  

The milk powder was reportedly confiscated in November, before it could reach stores.  The men were detained on Dec. 2 and formally arrested this week.  

The melamine-contaminated milk was shipped to Nanning Yueqian Food Additive Company in southern China’s Guangxi Province.  The company produces milk powder for big cities like Shanghai and Nanjing.  “We contacted Jinqiao immediately to inform them about the problem, but they denied it and sent us a report saying that the milk powder was already tested and turned out to be safe,” Chen Mingmei, a sales manager at Nanning Yueqian, told Xinhua News. “We didn’t trust them because last year’s Sanlu case was so heartbreaking.”

According to the World Health Organization, some companies add water to raw milk to increase its volume.  When the raw milk is diluted, it has a lower protein concentration. 

Companies using milk in products such as powdered infant formula normally check the protein level through a test that measures nitrogen concentration.  Adding melamine to diluted milk increases the nitrogen content of milk and the milk therefore appears to have a higher protein concentration–a concentration consistent with the protein concentration of milk before it has been diluted.  

In November, the Chinese government executed two milk producers who were responsible for last year’s nationwide melamine milk contamination scandal, which killed six infants and sickened over 300,000 in China.