The most expensive cheese in the world comes from Balkan donkeys. In 2016, a pound of pule cost as much as $1,700.

It’s not that the cheese possesses highly unusual qualities: It’s white with a crumbly texture and a flavor like strong manchego. No expensive ingredients are added during the cheesemaking process. The donkeys milked for the cheese aren’t wild, either. They’re domesticated and live on a farm in a Serbian natural reserve called Zasavica.

But donkey milk is exceptionally rare and difficult to produce. A jenny (female donkey) produces only about 1.5–2 liters of milk per day, while one cow produces up to 60 liters. Donkey milk also contains significantly fewer solids than cow milk, meaning far more milk is needed to make the equivalent amount of hard cheese. 

Costs of labor also influence pule’s sales price. Donkey milking—which occurs three times per day—must be done by hand, as no milking machinery exists to accommodate such a small, specialized industry.

Despite pule’s rarity and hefty price tag, its milk base is shockingly similar in nutritional makeup to a milk that millions have sampled free of charge: human breast milk.