Before refrigerators were invented, how did people preserve their food

Zeer or clay pot cooler was used, according to some archaeologists, up to 5000 years ago and is still used today.

The principle is simple: we all know the feeling of water on our bodies evaporating and making us feel cooler. Well, someone had the clever idea of using this effect to cool food.

A clay pot is placed into a larger one. Sand is placed into the gap between the pots. Food is placed into the smaller pot. The sand is made wet and a wet cloth is placed over the food. As the water in the sand evaporates it draws heat away from the food in the middle.

A simple idea but, like many simple ideas, absolute genius.