A 2000-Year-Old Refrigerator in the Desert

Over 2,000 years ago, people in the middle of the Persian desert actually made and ate ice. Initially, they'd haul ice from distant mountains, but it would melt away during the donkey ride, turning half of it into water. So, engineers decided to freeze it right there in the desert. They'd spread water in shallow pits on winter nights and block the sunlight with shaded walls. Even when the temperature wasn't below freezing, the water would freeze as heat radiated into the cloudless night sky. The challenge was storage. They dug deep pits in the ground and covered them with 18-meter-high earthen domes. This structure allowed hot air to escape through a hole at the top while cool air settled at the bottom. The walls were coated with a 2-meter-thick mixture of egg whites and goat hair to completely block heat. Thanks to this, they could buy ice from the market even in midsummer and make shaved ice desserts. This natural desert refrigerator is called a 'Yakhchal'.