The fact that you can eat hot pot in such a cold weather is inseparable from the efforts of the brewery

Hot pot and beer may seem like a normal combination on the table, but in fact, their relationship is much more complicated. What you may not know is that the fact that we can eat hot pot anytime and anywhere is inseparable from the efforts of breweries.

The reason why we can now break through geographical restrictions and enjoy the delicious beef, mutton, tripe, and yellow throat is inseparable from the developed cold chain transportation. Behind the cold chain transportation is modern refrigeration technology, and the widespread application of refrigeration technology is driven by breweries. Before that, we need to understand how beer is produced.

As the temperature drops in waves, the editor thinks about eating, fire, and hot pot after work.

When the north wind blows, it’s time to eat hotpot

There was a cold wind outside the window, and mist was rising inside. The bubbling pot bottom was filled with butter, and the lamb was curled at the edge, not to mention the tender tripe and crispy yellow throat. After eating, you will sweat profusely, and then finish with some beer. This is the right way to spend a cold day.

The fact that we can eat hot pot anytime and anywhere is inseparable from the efforts of the brewery. The delicious beef, mutton, tripe, and yellow throat that we enjoy are inseparable from the developed cold chain transportation. So what is the relationship between refrigeration technology and beer? Before that, we need to understand how beer is produced.

How is beer made?

Since beer has the word "wine" in its name, it is naturally inseparable from the fermentation of yeast. In simple terms, the process of brewing beer begins with germinating barley. Barley malt contains a rich amount of amylase, which can hydrolyze starch into monosaccharides (yeast cannot directly use starch). This step is called starch saccharification, and the resulting sugary liquid is called "wort". The next step is to filter the wort, add hops and boil it, cool it down, add yeast to ferment it, and filter it to get beer.

Simple diagram of beer brewing process | Source: Wikipedia

The most important step in brewing beer is fermentation. Depending on the fermentation method, beer can be roughly divided into three categories.

Ale: Ale refers to a type of beer fermentation technique. Ale yeast ferments on the top layer, with a short fermentation time and a relatively high fermentation temperature. The typical fermentation temperature of ale beer is between 20 and 22°C.

Lager: Lager comes from the German word Lagern (storage), so lager beer is also called cellar beer. Lager itself is also a kind of beer fermentation technique. Lager yeast ferments at the bottom, the fermentation time is long, and the fermentation temperature is low, about 7~13℃. Now most of the beer in the world is lager beer, because it has a low fermentation temperature, slow fermentation speed, easier to control quality, and suitable for large-scale mass production.

Differences in fermentation between ale and lager | Image source: justbeerapp.com

Naturally fermented beer (Wild): Use wild yeast in the air for natural fermentation. Natural wild yeast can completely consume the sugar in the wort, making this beer taste sour and "refreshing".

What is the relationship between refrigeration technology and beer?

The secret lies in the fermentation step. As we all know, fermentation generates a lot of heat, and the temperature of both ale and lager must be strictly controlled during fermentation, especially lager, which requires a relatively low fermentation temperature.

Before modern refrigeration technology, the production of lager required digging out the cellar for storage (this is the origin of Lager), and filling the cellar with ice from nearby lakes and rivers in winter, so that a lower temperature could be maintained in the summer. In order to avoid the influence of the summer heat, brewers would also plant chestnuts above the cellar, because the chestnut has a large crown and can provide enough shade, and its root system is shallow, so as not to damage the cellar. Even with so many measures, there were still many places in Germany that prohibited brewing beer in summer (how could there be such a thing?!).

Therefore, before the advent of modern refrigeration technology, lager beer could not be enjoyed all year round due to the fermentation temperature and was restricted by the seasons, and the production was not high. Therefore, in the 18th and 19th centuries, the scene of drinking iced beer in the summer was out of the question. Not only were there no air conditioners and refrigerators, but there was no beer either, leaving only the scorching heat.

History of Refrigeration Technology

When it comes to refrigeration, the first thing that comes to people's mind is ice. Ice is only available in winter, so people think of using ice cellars to store winter ice for use in summer. Ice cellars are usually built deep underground, and the soil is a good thermal insulation material. In winter, a lake or river with good water quality is selected, and ice is cut and transported to the ice cellar. The cellar entrance is sealed with grass, sawdust, etc. for insulation. Ice stored in this way will be lost. Once the cellar entrance is opened, all the ice must be used up, otherwise the ice in the ice cellar will not be preserved for too long.

Ancient ice cellars in Iran | Source: Wikipedia

In ancient times, in addition to using icehouses to store ice for cooling, there were also methods of cooling by using liquid evaporation to absorb heat. For example, in North Africa, a ceramic pot called Zeer was used for cooling.

Zeer pottery jar | Source: Wikipedia

How the Zeer pot works | Source: Wikipedia

Wet sand is filled between the inner liner and the outer shell of the pottery pot, and then a wet towel is placed on the pot. When the water in the sand evaporates, it will take away the heat, so that the food in the pottery pot can be kept at a relatively low temperature, which can be as low as 40℉ (4.4℃). From its principle, we can know that this kind of "refrigerator" should be used in arid places, such as North Africa, because the air there is dry, the dew point is low, and the water evaporates quickly, so that the temperature inside the pottery pot can be lowered.

As mentioned earlier, Germany needs to use ice to cool beer, but after the Industrial Revolution, the random discharge of sewage made it increasingly difficult to find clean natural water sources. Using unclean ice to cool the wine cellar may cause health problems. Using ice to cool the wine cellar is no longer feasible, and brewers are eager to have mechanical ice-making technology. Where there is demand, there is a market, and demand has given rise to mechanical refrigeration.

Mechanical Refrigeration

Modern refrigeration technology also relies on the principle of heat absorption through liquid evaporation, which can be seen from the invention process of the refrigerator.

Scottish professor William Cullen pioneered the study of evaporation of liquids in a vacuum in 1720. He then demonstrated a method of artificial refrigeration at the University of Glasgow in 1748 by boiling ether in a vacuum. Cullen designed a small refrigerator in 1755, using a pump to create a partial vacuum on a container of ether, which was then boiled, absorbing heat from the surrounding air. This experiment produced a small amount of ice, but it was not practical.

The boiling point of ether is 34.6℃, and it is very easy to evaporate. Ether is encapsulated in the drinking bird. The glass bubble on the head is covered with a wet sponge. Due to the evaporation of water, the temperature drops, resulting in low air pressure in the glass bubble, which absorbs the ether into the head, making the bird top-heavy.

In 1805, American inventor Oliver Evans described a closed vapor compression refrigeration cycle that produced ice by evaporation of ether under vacuum. In 1834, Jacob Perkins built the world's first operational vapor compression refrigeration system, but it was not commercially successful. The first practical vapor compression refrigeration system was built by James Harrison, a British journalist who emigrated to Australia, and his 1856 patent was for a vapor compression system using ether, alcohol, or ammonia.

Vapor compression refrigeration | Source: Wikipedia

In 1870, S. Liebmann's Sons Brewing Company in Brooklyn, New York, first used mechanical refrigeration. By 1891, almost all breweries used mechanical refrigeration. Mechanical refrigeration allowed breweries to produce beer all year round, and lager beer, which is suitable for large-scale production, became popular, which is why most beer is lager now. Thanks to modern refrigeration technology, lager beer is mass-produced and available to ordinary people.

Later, modern refrigeration technology was also adopted by meat processing plants and dairy processing plants to preserve meat and dairy products, allowing areas with underdeveloped dairy and livestock industries to enjoy the taste of meat. In this way, fresh food, which also benefits from modern refrigeration technology, magically meets beer on the table and becomes a wonderful combination on hot pot. When you eat hot pot with your good friends in the future, you might as well tell them the story between hot pot and beer.

Source: Institute of Physics, Chinese Academy of Sciences