China’s once-notorious “gutter oil”, recycled from kitchen and drainage waste, has almost vanished from dining tables in recent years and now carries the nickname liquid gold. The substance has become a highly sought-after feedstock for producing clean energy, especially sustainable aviation fuel (SAF), with biofuel producers such as Hong Kong-based Ecoceres sourcing gutter oil across the Greater Bay Area. EcoCeres’ co-chairman, Alan Chan Ying-lung, witnessed how the restaurant waste transformed...