food is a necessity for human survival, so food preservation has become one of the oldest technologies used by human beings. Strawberry decay
fresh strawberries bought from the supermarket, put into the refrigerator for two days, some parts began to rot or moldy, this is because of the high moisture content and thin skin of strawberries, very vulnerable to damage and softening and decay.
strawberry is usually soaked in calcium lactate solution to keep fresh. It is difficult to judge which preservative is sprayed from the appearance, but they are harmless to human body. However, this kind of preservative is not very durable. Strawberries face the fate of rotten head and rotten tail.
when cleaning strawberries, you can add a few drops of apple vinegar or white vinegar in clean water, and gently rub the surface of strawberries to remove most of the preservatives. It can also keep the strawberries in the refrigerator fresh and not easy to rot.
2. Banana turns black
due to its own characteristics, banana will grow a little bit after exposure for a few more days; Black spots;, A lot of people don’t dare to eat.
the epidermal cells of banana contain an oxidizing enzyme. It is tightly wrapped by the cell membrane. However, once it is squeezed or frozen, the cell membrane breaks, and the oxidizing enzyme flows out and oxidizes, a black compound will be formed.
as long as the banana stalks are wrapped with fresh-keeping paper to reduce the exposure to air and release ethylene with ripening effect, the storage time can be prolonged, and it is more effective to wrap several stalks separately.
3、 Tea is affected by damp
people who like to drink tea believe that there is a lot of tea in the cupboard. Some improper storage, poor sealing of tea, easy to damp and deterioration, unable to taste the most original aroma.
tea; Moisture absorption & quot; Many people expose the damped tea to the sun, which will make the tea taste bad. The best way is to use a clean pot, stir fry the tea slowly until the moisture disappears, and then seal it up after cooling, so as to reduce the loss of tea aroma.
4. The bread is hard and dry. Once the bread is not properly collected, it will get moldy. If it is not found and eaten, it is easy to cause gastrointestinal revolution.
in addition, a whole loaf of bread can not be eaten in three or two days, so it is easy to become dry and hard after a long storage time. How to solve this problem?
put one or two sections of celery in the bread package and seal the bag tightly. The moisture content can make the bread comfortable at any time; Moisturizing & quot; Keep fresh and ready to eat soft bread.
5、 Meat vacuum packaging
pork, chicken, salmon, etc. are always hard, frozen and caked when they are taken out of the freezer. Thawing also takes a long time.
how to keep fresh meat durable and better quality?
first, fill a large container with clean water. Next, put the fresh meat in the sealed bag and close the sealing strip, leaving only a small opening.
put the sealing bag into the water, squeeze out the air in the bag by water pressure until the sealing strip is close to the water surface, and then completely seal the bag to achieve the effect of vacuum packaging.
at this time, you can see that there is little air left in the bag. After wiping the moisture on the outside of the bag, it can be stored in the refrigerator to keep the food fresh for a long time.
preservation technology: 6667
refrigeration and freezing 6667
refrigeration and freezing is perhaps the most widely used way of food preservation today. The purpose of refrigeration is to slow down the bacteria so that food can be kept longer (about a week or two, not just half a day). The purpose of freezing is to prevent all bacteria from acting, because bacteria will completely lose their activity under freezing conditions.
refrigeration and freezing is suitable for almost all kinds of food: meat, fruits, vegetables and beverages. Generally speaking, cold storage has no effect on the taste and texture of food. Freezing has no effect on the taste and texture of most meat, and has very little effect on vegetables, but it can completely change the texture of fruit (the flesh will become paste). Because cold storage has little effect on food, it has been widely used.
since about 1825, canning has become a way for people to preserve food, and the preservation time is quite long. In the process of canning, the food is boiled in the can to achieve sterilization effect, and then sealed (before or when the food boils), so that no new bacteria enter. As the food in the can has been completely sterilized, it will not go bad. Once you open the can, bacteria will enter and invade the food, so you must & lt; Please refrigerate after opening（ It’s on many food labels & mdash& mdash; This indicates that the food in the package is sterile before opening.
we usually think & lt; Can & quot; It’s made of metal, but actually many sealed containers can be used to make cans. For example, glass bottles can be boiled, sterilized and sealed. Soft bags and boxes made of foil or plastic can also be used. The boxed milk on the shelf is & lt; Canned & quot; Milk. The milk in the box is sterilized (by ultra-high temperature instantaneous sterilization) and sealed in the box, so the milk will not deteriorate even at room temperature.
canned food has a disadvantage, that is, the taste and texture of the food will change during the boiling process (along with the nutrients), which is why people prefer to refrigerate or freeze.
Many foods are preserved by dehydration. When you walk into any grocery store, you can see these dehydrated products:
1. Milk powder
2. Boxed dehydrated potatoes
3. Dried fruits and vegetables
4. Air dried meat (such as beef jerky)
5. Soup powder and sauce powder
6. Italian noodles
7. Instant rice
. Most bacteria will die after drying, Or completely inactivated, so dehydrated food can be stored in sealed condition for a long time.
generally, complete dehydration changes the taste and texture of food. But in many cases, complete dehydration can also create a whole new kind of food that people like as well.
freeze drying preservation
freeze drying (freeze drying) is a special drying technology, which can achieve the purpose of preservation by removing the moisture in food, but the effect on the taste of food is much less than the general dehydration technology.
in the process of freeze-drying, food should be frozen first, and then placed in a high vacuum. In this way, the water in the food will sublimate & mdash& mdash; In other words, water changes from solid ice to water vapor. Freeze drying technology is often used to make instant coffee, and also has a good effect on the preservation of fruits (such as apples).