What are truffles, and why are they so expensive?

Dig into the truffle’s unique and mysterious biology to find out what makes them so rare and the limitations of farming them.

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Truffles are one of the world’s most expensive foods— in part because global demand often outstrips supply. And truffles are becoming even more rare and more expensive as deforestation and climate change shrink their suitable terrain. But why are these fungi so rare? And why don’t we just farm more of them?