In fact, human use of refrigeration can be traced back to thousands of years ago. If we want to divide an interval, we can basically regard the ancient refrigeration wisdom as the era of natural refrigeration. The "ice room" storage is one of the earliest natural refrigeration methods, that is, storing ice in winter, putting it in the ice room and enjoying it in summer.

This refrigeration technology is primitive and simple, but it is very easy to use. From thousands of years ago to the19th century, people have been using it.

Ice cubes need to absorb heat to melt, so the freezer should be built in a cool place, isolated from the outside world. Generally speaking, the ice bank is like a semi-basement, partly underground, built near natural ice sources such as rivers and freshwater lakes, which is convenient for mining and storage.

At the same time, people will cover the ice with sawdust, which has poor thermal conductivity and can be regarded as a heat protection layer on the ice. This will keep the ice cubes for several months, and even properly handle them until the next winter.

Many ancient civilizations invariably used this method to store ice cubes, and China was one of them, and it was completed around 1000 BC. There is a fragment in the written record that "the ice was smashed the next day, and the ice was sucked in Lingyin the third day".

In the Song Dynasty, an ice well service was set up to store ice cubes. There are many kinds of iced food, such as mixing sugar, fruit and juice in ice cubes, and some people added fruit pulp and milk in the Yuan Dynasty.

Now some street names can also see the historical traces left by the igloo:

It is worth mentioning that in China, the supporting facilities for storing ice cubes are very particular, such as the "ice guide", which is usually called the ancient refrigerator:

(bronze ice guide in the Warring States period)

Its appearance is simple and generous, and its internal structure is ingenious. Interestingly, in summer, people can put ice cubes in the bronze ice guide, so that the drinks in the wine-holding area will get cold, which becomes an iced drink to cool off the heat.

But if you can heat the water in winter, the wine will turn into warm wine. ....

In my opinion, this is not only wisdom, but also art.

Romans and Jews also have a soft spot for mixed iced drinks. Among them, Rome would take snow from the mountains and then store it in pits and cover it with similar insulation materials.

But in areas where the air is dry, such as Egypt, people will choose another cooling method, evaporative cooling.

As we know, evaporation can absorb heat and has a cooling effect. This physical phenomenon was discovered by humans long ago and applied to refrigeration.

The water on the ground is evaporating.

In a hot climate, food will not be preserved for a long time, and it is difficult for some fruits and vegetables to last for a week. So people will use this technology to make fresh-keeping tools for their own food, which is generally called zeer.

This is an "ice" box composed of two clay pots. Some people call it a refrigerator in a pot.

Zeer is very simple to use The small pot is nested in the big pot, and the gap between them will be filled with sand.

Then add water to the sand to keep it moist.

At this time, the outer tank will generally have multiple holes to facilitate ventilation, and the inner tank will generally make some local materials for waterproof facilities, and the whole device will be placed in a ventilated and dry place.

Finally, put some unsalable foods, such as vegetables and fruits, into the inner tank, cover it with wet cloth, and then enter the cold storage mode.