It turns out that you are this kind of hot pot: How does a self-heating hot pot “self-heat”?

Hotpot, as one of the traditional Chinese delicacies, is accepted and loved by consumers for its convenient and fast cooking method and unique flavor. It is a gourmet dish suitable for all ages. The types of hotpot we often eat include the Chongqing Southern Hotpot, which is famous for its "numbing, spicy and hot" taste, and the Northern Hotpot, which is mainly represented by shabu-shabu mutton. So, did our ancestors also like to eat such delicious hotpot?

The answer is yes. Hot pot, known as "Gudong Geng" in ancient times, got its name from the "gulp" sound made when food was put into boiling water. The historical book "Han Shi Wai Chuan" records that in ancient times, people would "beat the bell and set up the tripod" to eat during sacrifices or celebrations. That is, everyone would sit around the tripod, put the ingredients into the tripod bell, cook them, and share them. Many scholars believe that this can be regarded as the embryo of hot pot.

The development of hot pot has changed according to the utensils of the time, social needs and the discovery and introduction of raw materials. The predecessors of the modern popular mandarin duck pot and nine-grid pot are the "five-cooking cauldron" mentioned by Emperor Wen of Wei, which can cook a variety of foods at the same time.

Nowadays, with the advancement of technology and the development of cooking skills, hot pot varieties and cooking methods have also become more diverse. A new type of instant food, self-heating hot pot, has also come into our sight. This simple version of hot pot, which does not require plugging in electricity and can be automatically heated by just pouring a cup of cold water, is becoming more and more popular among consumers.

The principle of self-heating hot pot heating

The heating principle is not complicated. It mainly uses the contact between the substance in the heating bag and water. In this process, a large amount of heat is released, and the air in the closed space continues to heat up, the temperature can reach more than 150℃, and the steam temperature can reach 200℃. As a result, the food in the upper food box absorbs heat and heats up quickly.

The heating pack mainly contains sodium carbonate, roasted diatomite, iron powder, aluminum powder, coke powder, activated carbon, salt, quicklime and other ingredients. Quicklime is added with water to produce slaked lime, which emits a lot of heat energy. At the same time, iron powder and aluminum powder can form a galvanic cell effect with activated carbon, water and salt, releasing a lot of heat through redox reaction.

In addition, diatomaceous earth has a loose and porous structure and is often used as a desiccant to absorb water. During the heating process, diatomaceous earth can absorb some of the water, allowing them to fully contact and react. Salts such as sodium carbonate are mainly used to absorb trace amounts of infiltrated water, prevent quicklime from gradually becoming ineffective, and play a certain auxiliary role in chemical reactions.

Although self-heating hot pot is convenient and quick, it does pose certain safety risks. The heating pack of self-heating food is flammable and explosive and should be kept out of the reach of children to prevent children from blindly using the heating pack and causing danger.

Consumers must be very careful when using it, and it is not allowed to be carried on trains or planes.

Please note when operating:

1. Only cold water can be added to the heating pack. Do not pour hot water on the heating pack for quick results. Hot water can easily cause a violent reaction between the substances in the heating pack and the hot water, causing the heating pack to expand or even rupture, and may even cause an explosion.

2. When heating, do not place it on a glass or plastic table to prevent the glass from breaking. Because the bottom temperature of the self-heating hot pot is very high when heated, if it is placed on a table that is not resistant to high temperatures, it may cause the table to crack. There are vents on the lid. When using it, make sure the vents are open so that it has a place to release pressure. And do not add a cover to prevent expansion and explosion accidents.

3. Do not use a hot pot in a confined space. When the hydrogen generated by heating reaches a certain concentration, there is a risk of explosion once it encounters a fire source.

4. Do not use the self-heating bag if it is damaged. Before discarding the heating bag after use, let it react with water. If you are not sure, you can consider wrapping it in a plastic bag before throwing it away. Otherwise, water or rainwater will enter the narrow trash can and react to produce hydrogen. Although the amount of hydrogen is small and easy to diffuse, the calcium hydroxide produced is corrosive.

When purchasing self-heating products, it is best to choose a plastic box made of PP5 material. And strictly follow the instructions and enjoy them on a high-temperature resistant table. After heating is completed, be careful when opening the lid to avoid being burned by steam. Finally, after enjoying the self-heating hot pot, sort and dispose of food packaging and leftover food.

The article is produced by Science Popularization China-Starry Sky Project (Creation and Cultivation). Please indicate the source when reprinting.

Author: Liu Junling, Exhibition Instructor at Xinyu Science and Technology Museum

Reviewer: Zhang Na, Associate Researcher, Doctoral Supervisor, Peking University School of Public Health