Those who know how to cook go to the vegetable market: they want to buy everything they see! Buy, buy, buy, buy!
After I got home, I filled up the refrigerator and kept it ugly. The point is that after a few days, the ingredients are half-broken…
In fact, many people have a big misunderstanding of refrigerators. Refrigerators are not safes. Putting ingredients in is not foolproof.
Wrong preservation methods can not only extend the preservation time of ingredients but may also directly advance its “dead period”…
Different ingredients have different “spleen”, we have to choose the appropriate preservation method and preservation environment according to their “spleen”.

(1) Why does food rot?
If you want to keep food fresh, you must first understand the reasons for food spoilage and rot.
Generally speaking, there are four main reasons.
1. It is caused by microorganisms.
In the process of production, processing, transportation, and storage, food may be contaminated by ubiquitous microorganisms in the environment. The growth and reproduction of microorganisms can decompose nutrients in food, and finally decompose protein in food into peptides and organic acids, resulting in ammonia odor and sour taste. At this time, the food also loses its original toughness and elasticity and makes the color abnormal.
2. Is the role of enzymes.
Foods often contain lipases, proteases, amylases, polyphenol oxidases, and peroxidases. The effects of these enzymes will accelerate the metabolism of foods and promote the gradual deterioration of foods. The daily rancidity of rice and fruit rot is the fermentation caused by the decomposition of carbohydrates by enzymes.

3. Is the chemical reaction of food.
Many fats and oils in food have unsaturated bonds in their molecular formulas. These bonds are very unstable and are easily oxidized, resulting in a series of chemical reactions. The oxidized fats have a strange smell, such as fat turning from white to yellow. For fruits and vegetables, vitamin C and natural pigments (such as tomato pigments, etc.) will also be oxidized, which will reduce the quality of the fruit and even deteriorate.
4. Moisture.
Dry foods can easily absorb moisture in the air and become damp, resulting in poor taste, and even mold and mildew on the food. Spoiled food not only changes its appearance, loses the original food’s color, aroma, and taste quality, and its nutritional value is reduced, but it also contains corresponding toxins that endanger human health.
Therefore, food preservation can start from these points. Simply put, it is to destroy the living conditions of microorganisms, avoid exposure to food materials in the air, reduce enzyme activity, and prevent food from oxidation and moisture.

(2) Common fresh-keeping methods and principles
Under normal circumstances, we will use the following 4 more commonly used methods.
1. Cryopreservation
Within a certain period of time, cryopreservation can inhibit the activity of microorganisms and enzymes in food and slow down food spoilage. Low-temperature storage can be divided into two methods: refrigeration and freezing, and refrigerators are generally used.
2. Vacuum storage
It is also called decompression packaging, which is to extract all the air in the packaging container and seal it to maintain a high degree of decompression in the bag. The scarcity of air is equivalent to the effect of low oxygen so that most microorganisms have no living conditions. At the same time, it also isolates the contact of bacteria from the outside world to extend the preservation period of food.
3. Dehydration and drying
Dehydration drying refers to reducing the moisture content of foods, inhibiting the growth of spoilage microorganisms, and keeping foods at room temperature for long periods of time through methods such as sun drying, drying in the shade, drying, and smoking. Dried sweet potatoes, dried beans, dried chilies, bacon, and dried intestines are all applications of dehydration and drying.

4. Chemical preservation
Chemical preservation mainly includes sugar, salt, and vinegar. Generally, the salt concentration reaches 10%, which can inhibit most of the microorganisms but cannot kill the microorganisms. The sugar content of candied food must reach 60%-65%. This kind of food should also be stored in a sealed and moisture-proof condition, otherwise, it is easy to absorb water and reduce the anti-corrosion effect. Common salted fish, bacon, pickled vegetables, preserved fruits, preserves, etc. Vinegar can increase the hydrogen ion concentration and is mostly used in various vegetables, such as kimchi and pickled cabbage.
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