There are two main types of biofuel — ethanol, an alcoholic binding agent made from plant material such as corn starch or sugar, and biodiesel, a nontoxic and biodegradable liquid fuel derived from animal fat, cooking grease, or vegetable oil. Ramen is one potential source of the latter type and has made its way into the tank of a Japanese locomotive.

In 2022, a sightseeing train operated by Amaterasu Railway Company switched over to biodiesel fuel that's made from tempura cooking oil and lard extracted from leftover ramen broth. The mixture costs almost the same as diesel does and works just as well, yet it fills the air with the scent of stir-fried food instead of black fumes.

Transforming leftover ramen into biofuel is a good way to counteract food waste and is part of a movement in Japan that aims to cut the nation’s food waste in half by 2030. Amaterasu general manager Hiroyoshi Saitoh stated that in addition to serving as a tourist attraction, their trains help people "to become more conscious about environmental issues as well as biodiesel."