SHANGHAI - Shanghai-based Bright Dairy & Food is recalling a batch of its Ubest-brand milk products after an investigation revealed that the products may have been contaminated with lye, according to the city's quality and technical supervision bureau.

An investigation conducted by the bureau Wednesday found that food-grade lye that was used to clean pipes had leaked into and contaminated a production line at one of the company's plants on Monday, a bureau spokesman said early Thursday.

The contamination was caused by a mechanical malfunction during regular maintenance procedures, said the spokesman.

The Shanghai-listed company said in an earlier statement that it had removed the milk, sold in 950-ml packages, from retail shelves and tried to recover those that had already been sold to customers.

The bureau will analyze and evaluate Ubest milk products produced on Monday to look for possible safety hazards, according to the spokesman.

China's dairy industry suffered a major blow in 2008 following an incident in which melamine-tainted milk produced by the Sanlu Group killed six infants and left more than 290,000 others with kidney damage.