In the mid-20th century, if you were spreading margarine on your toast, there was a good chance it contained whale oil.

As odd as it sounds today, whale fat was a common ingredient in margarine, especially in Europe from the 1930s through the early 1960s. It was cheap, abundant (thanks to industrial whaling), and easy to process into a semi-solid fat.

Of course, whale oil had a…distinct aroma. Manufacturers used chemical treatments to deodorize and bleach it, transforming it into something more palatable. The result: a spreadable, buttery alternative made from the ocean’s largest mammals.

Whale oil quietly disappeared from margarine by the late 1960s, thanks to the rise of plant-based oils—and growing awareness of whale conservation.