Today many people are doing two things: testing nucleic acid and stockpiling goods...

Just yesterday, Beijing announced that Chaoyang District had designated 14 lockdown areas, and Shanghai immediately began frantically teaching Beijing residents how to stock up.

In the evening, under the atmosphere created by the "atmosphere group", many friends in Beijing really started to stock up on goods.

Looking through the circle of friends, the goods that everyone is stockpiling are also diverse.

Needless to say, necessities such as vegetables, fruits, and water are available. It was circulated in the group that a reporter had stored a lot of water at home and even planted vegetables.

Some people who are better off have already stocked up their supplies in freezers.

Those who don’t trust their cooking skills have stockpiled a lot of jarred chili peppers, Lao Gan Ma, and Wang Shouyi’s marinade ingredients.

Of course, there are also many people who stock up on some addictive items, such as cigarettes and alcohol. Tadpole's roommate showed off the 6 packs of cigarettes he had just received.

Image source: Tadpole Jun

Of course, many people have also stockpiled a lot of food with a long shelf life, such as freeze-dried vegetables. After all, fresh vegetables are not the first choice for stockpiling vegetables (unless there is a freezer), and freeze-dried vegetables are relatively easier to stockpile, and freeze-dried food has a place in the so-called "doomsday food" family.

01

Humans have been developing a "doomsday package"

Food spoilage is mainly due to the growth of microorganisms. Bacteria, fungi and some enzymes decompose the protein and sugar in food, which then makes the food sour, rotten and even produces toxins. There are many reasons for the growth of microorganisms in food, such as moisture, nutrients, temperature, pH and so on.

From ancient times to now, people have been studying ways to extend the shelf life of food. But for the ancients, they did not understand temperature, pH, and water content, which were the only factors they could control.

In order to reduce the proportion of water in food, ancient people really tried every possible way: drying with fire; drying in the sun; drying in a ventilated place; burying under the snow to freeze dry; pickling with large amounts of salt or sugar... In this way, meat, seeds, and a small number of vegetables and fruits were stored to prepare for unexpected needs.

During World War I, as the demand for field food increased, people found that many soldiers died of enteritis and dysentery. This was because the soldiers' food contained too much meat and salt, and the vegetable content was seriously insufficient. However, fresh vegetables were extremely difficult to transport and preserve, so people came up with a solution: dry and dehydrate fresh vegetables, and when eating, just add hot water to soften the dried vegetables. This kind of dried vegetables is the prototype of the dried vegetables we see in instant noodles today.

Image from Taobao

However, this type of dried vegetables still has disadvantages - because most of the vitamins and trace elements in the vegetables will be lost during the drying process. In 1960, during the Apollo space program, NASA invented the "freeze-dehydrated vegetable technology" to enable astronauts to eat vegetables and supplement vitamins in space. This technology removes excess water from vegetables, while retaining the chlorophyll and vitamins contained in them, making them easier to store, preserve and transport.

02

How are freeze-dried foods made?

We all know that water has three forms: gas, liquid and solid. When water is at a temperature of 0.01°C and a pressure of 0.610KPA, it will present a situation where gas, liquid and solid coexist. The temperature and pressure of water at this time are also called the triple point of water. During the phase change process of water, when the pressure is lower than the triple point pressure, solid ice can be directly converted into gaseous water vapor, which is the sublimation of ice crystals.

Freeze-dried food utilizes this principle. Through a special freeze dryer, under vacuum conditions, the moisture in frozen vegetables, fruits, meat, aquatic products and other foods is directly sublimated from solid ice into gas, thereby dehydrating the food.

Freeze-dried food still looks the same as it originally did, but because it has lost almost all its water content, it feels like holding a piece of Styrofoam in your hand. However, after adding water, not only can the shape and feel of the food be restored, but the taste is also the same.

03

Why can freeze-dried food be preserved?

The original form and taste of the food?

This is because freeze-dried food is dehydrated under freezing conditions. The shape of the food after freezing is fixed. Without destroying the original skeleton structure of the food, the tiny ice crystals filling the gaps in the skeleton are sublimated and dehydrated. The dehydrated food not only maintains the original skeleton structure, but the space occupied by the original ice crystals will form sponge-like micropores. These micropores can easily absorb water, allowing the food to be quickly restored.

In addition, freeze-dried food is processed under low temperature and vacuum conditions. The original pigments and aromatic substances will not be oxidized or destroyed, and no preservatives need to be added during the freeze-drying process. This maintains the "original flavor" of the food to the greatest extent and retains 98% of the nutrients in the food.

Seeing this, some people may ask, what are the disadvantages of freeze-dried food?

For traditional drying technology, freeze-dried food has more processes, more complicated equipment operation, low yield and high price. For those foods that are not resistant to cold, the taste will still change during the freezing and dehydration process.

But as a food storage, the advantages of freeze-dried food are unquestionable.

Tips: What should you stock up on if you really want to?

We have all read the various guides, and I believe everyone has received the stockpiling suggestions from the people of Shanghai. So when the time comes to respond to an emergency, what should we stockpile?

In fact, in addition to food, there are many things we really need to stock up. Below is a family emergency kit poster produced by the Central Bank. Let’s take a look.

Source: CCTV News

But then again, I am not stockpiling any goods at the moment, because I am still very confident in Beijing. The Beijing Daily also said that Beijing supermarkets have sufficient supplies. On the other hand, it is mainly because wallets won’t pay.

Finally, I would like to give Beijing residents a heartfelt suggestion on hoarding food: when hoarding, don’t hoard your favorite food, otherwise, what you hoarded yesterday will be eaten up today…

Reminder from Tadpole's colleague

References

【1】Huang Jinsong, Zhou Yibin, Du Xianfeng, et al. Research progress of dehydrated vegetables[J]. Food Industry Science and Technology, 2006(04):107+198-201.

【2】Guo Zhendong. New technology for food dehydration—vacuum freeze drying[J]. Food and Drug, 2004, 6(1):32-33.

Zhang Bingwen, Hao Zhenghong. Application of low temperature vacuum frying and dehydration technology in food processing industry[J]. China Business Industry, 1999(12):33-34.

【3】Chen Liuji, Jin Mingfeng. Application of high technology in food dehydration industry[J]. Guangzhou Food Industry Science and Technology, 1998(1):10-12.

END

Tadpole Musical Notation original article, please indicate the source when reprinting

Editor/Heart and Paper