Everyone has this experience, and the sweet potato that has been put for a long time is always sweeter than the newly dug one. What is the reason?

We can intuitively see that sweet potatoes have been stored for a long time, the water content has decreased a lot, and wrinkles have appeared on the skin. The decrease of water has a great influence on the improvement of sweetness for two reasons: First, the decrease of water evaporation increases the sugar concentration in sweet potato. Second, in the process of placing, water participated in the hydrolysis reaction of starch in sweet potato, and the starch was hydrolyzed into sugar, which increased the sugar in sweet potato. So we think the sweet potato with a long history is sweeter than the newly excavated sweet potato.

It is not advisable to burn oil and smoke when cooking.

When cooking, some people like to burn the oil to smoke or even burn it before putting the vegetables, especially when using vegetable oil, thinking that if you don't burn the "dead" vegetables, there will be oil and gas. It should be pointed out that this is a bad practice. Oil is easy to form polycyclic compounds at high temperature. Generally, vegetable oil contains more unsaturated fatty acids, which makes it easier to form polycyclic compounds. Experiments show that polycyclic compounds are easy to induce animal bladder cancer. Generally, as long as the oil is boiled, the "internal heat" of the oil can be removed.

Practical value of salt

Salt is not only an important chemical raw material, but also an important condiment in human life. In addition, salt has many uses.

(1) Drinking a cup of salty boiled water in the morning can cure constipation. Drinking salty boiled water can cure sore throat and toothache.

(2) Eating by mistake is toxic, and drinking salty boiled water has detoxification effect.

(3) gargling with light salt boiled water every day can prevent various oral diseases.

(4) When taking a bath, adding a small amount of salt to the water can make the skin firm.

(5) Tofu goes bad easily. For example, if salt is dissolved in boiling water, tofu can be preserved for several months even in summer.

(6) Peanut oil contains water, which will stink if it is left for a long time. You can fry the salt, let it cool, and add salt according to the ratio of 40 kg oil 1 kg salt, which can keep peanut oil smooth and delicious for 2-3 years.

(7) Flowers can be inserted in light salt water for several days.

(8) Newly bought glassware, boiled with salt, is not fragile.

(9) When washing colored clothes, soak them in 5% salt water for 10 minute, and then wash them, so that the color will not fade easily.

(10) When washing white clothes with sweat stains, rub them with 5% salt water first, and then wash them with soap, so that yellow sweat stains will not appear.

(1 1) Mash carrots, mix them with salt, and wipe the blood on clothes.

(12) Bronze is rusty or has black spots, which can be wiped off with salt.

Why do mung beans turn black after being cooked in an iron pot?

Mung beans will turn black after being burned in an iron pot; After apples and pears are cut with iron knives, their surfaces will also turn black. This is because the cells of mung beans, apples, pears and various fruits all contain tannic acid, which can react with iron to produce black iron tannic acid. When mung beans are cooked in an iron pot, they will produce some black iron tannins, so they will turn black. Sometimes, pears and persimmons will have some black spots on their skins even if they are not cut with an iron knife. This is because tannic acid molecules contain many phenolic hydrocarbon groups, which are very sensitive to light and are easily oxidized by oxygen in the air and become black oxides.

Milk should not be cooked at high temperature for too long.

Milk is rich in protein. When heated, colloidal protein particles will change greatly. When the temperature of milk reached 60-62 degrees, slight dehydration began, and protein particles changed from sol state to gel state, resulting in precipitation.

Milk also contains unstable phosphate. When heated, acidic calcium phosphate becomes neutral calcium phosphate, which will also be precipitated in the form of insoluble precipitate. In addition, when the milk is heated to about 100℃, the lactose in the milk begins to coke, which makes the milk have leg color and gradually decomposes into lactic acid, and at the same time produces a small amount of formic acid, which makes the milk sour. So don't boil the milk for too long.

Bactericidal effect of garlic

Garlic is rich in protein, fat, sugar and vitamins A, B and C, etc. Garlic seedlings also contain calcium, phosphorus, iron and other ingredients. Garlic has strong bactericidal power, because garlic contains garlic oil, which is mainly composed of propylene sulfide, and also contains a small amount of propylene disulfide and propylene disulfide.

Allicin will decompose when it is heated by alkali, so raw garlic should be used for anti-inflammatory and sterilization, and it can't be used with alkaline substances.

Garlic tastes in your mouth after eating it. You can put a little tea in your mouth and chew it carefully, or you can put a piece of sugar in your mouth to reduce the garlic flavor.

Can't drink boiled water.

The water used for steaming steamed bread or side dishes at home is called boiler water. This kind of boiler water can't be drunk, nor can it be used for cooking rice or porridge. What is the reason?

As we all know, water contains trace amounts of nitrate. When water is heated for a long time, the concentration of nitrate increases relatively due to the continuous evaporation of water, and it is decomposed into nitrite by heating.

Nitrite does great harm to human health. It can denature hemoglobin in human blood, so that it can no longer combine with oxygen, leading to early hypoxia. Nitrite can also reduce human blood pressure, which can lead to collapse in severe cases. Modern medicine has proved that nitrite is also a strong carcinogen. Therefore, boiler water cannot be drunk.

How to remove the bitterness of fish gall

People like to eat fish because it tastes delicious. However, if you accidentally break the gallbladder when cutting fish and bile sticks to the fish, it will make the fish bitter and affect people's appetite.

Bile acid is the main component of bitterness in bile, because it is insoluble in water, so it is difficult to wash away bile that has penetrated into fish with water. Sodium carbonate can react with bile acid, and the product is sodium cholate, which is easily soluble in water. Therefore, if the fish bile is broken, just put some baking soda powder on the fish with bile and rinse it with water later, and the bitterness can be eliminated. If the bile pollution area is large, fish can be soaked in dilute alkali solution for a while, and then washed, and the bitterness can be completely eliminated.

Four taboos for drinking soybean milk

1, avoid washing eggs: mucin in eggs is easy to combine with trypsin in soybean milk, producing a substance that is not absorbed by the human body, thus losing its nutritional value.

2, avoid cooking: soybean milk contains trypsin inhibitor, if not cooked thoroughly, people will have symptoms such as nausea, vomiting, diarrhea.

3. Avoid brewing brown sugar. Because the organic acid in brown sugar can combine with protein in soybean milk to produce "denatured precipitation powder", brown sugar is forbidden to brew, while white sugar has no such phenomenon.

4. Avoid excessive drinking: If you drink too much soybean milk at one time, it will easily lead to "protein's indigestion due to overeating" and symptoms such as diarrhea and abdominal distension.

Why not add cold water between roast meat and bone soup?

Meat and bone soup is nutritious and delicious, mainly because protein and fat are dissolved in the soup. When stewing meat and bone soup, first put it in the pot with cold water, gradually raise the temperature and boil it, and then simmer it with slow fire. This can loosen the bone tissue of meat and bone, and gradually depolymerize and dissolve protein and fat in bone. As a result, the meat and bone soup is more simmering and thicker, oily as cream and chewy.

If water is added in the middle of stewing, the temperature of meat and bone soup will suddenly change, which will lead to the rapid solidification of protein and fat, which will shrink into a ball and no longer disaggregate. In this way, the gap on the surface of bone will be narrowed, leading to the contraction of bone tissue, which is not easy to burn brittle, and the protein and fat in bone marrow can not be dissolved in large quantities. At this time, the protein fat in the soup will be reduced accordingly, thus affecting the delicacy of the soup.

Tofu had better not be cooked with spinach.

Spinach is rich in nutrition and is known as the "king of vegetables", but it contains a lot of oxalic acid, which is about 300 mg per 100 g of spinach. Tofu contains more calcium. If both enter the human body at the same time, chemical changes can occur in the human body to generate insoluble calcium oxalate. Stones in the human body are deposited by insoluble calcium salts such as calcium oxalate and calcium carbonate, so spinach and tofu should not be eaten together. In addition, eating spinach alone should not be eaten too much at a time, because oxalic acid in spinach can combine with calcium and iron in the human body, which makes the human body lack calcium and iron and affects health.

When the ratio of calcium to oxalic acid is 1: 2, stones are most likely to form. If the food mix destroys this ratio, stones can be prevented. For example, eating spinach with sesame seeds, milk or fish rich in calcium can overcome this shortcoming of spinach.

The stunt of pressure cooker

Anyone who has used a pressure cooker knows that cooking with it saves time and oil, and there is less nutrient loss, especially the rice cooked with it is particularly delicious. Why?

We know that the main component of rice is starch, which contains 17% amylose and 83% amylopectin. Amylose is soluble in hot water, while amylopectin is insoluble in water, but it can absorb water and gelatinize into a very viscous solution in hot water. Therefore, the viscosity of rice mainly depends on the gelatinization degree of amylopectin, and the gelatinization degree of amylopectin depends on the temperature in the pot when cooking.

Ordinary aluminum pot cooks in the plain area, the steam pressure in the pot is only one atmosphere, and the boiling point of water is 100 degrees, but the pressure cooker is different, with working pressure 1.3 kg/cm2 and working temperature 124 degrees. Because the cooking temperature of pressure cooker is higher than that of ordinary rice cooker, it can dissolve more amylose and gelatinize amylopectin. At the same time, because the pressure cooker is cooked in a sealed state, the aroma loss of rice is less, so the cooked rice is sticky, fragrant and delicious.

Why do you shed tears when you cut onions?

Onions are native to West Asia and were discovered as early as 3000 years ago. Because of the low requirements for growth conditions, he quickly crossed the ocean and settled in many places. Nowadays, it has become a common vegetable in the market.

According to chemical analysis, onion contains a very irritating substance-n-propyl mercaptan. After peeling or slicing onions, the n-propyl mercaptan in them volatilizes into the air. If it slips into people's eyes, it will stimulate the lacrimal gland and make people cry.

How to overcome it? N-propyl mercaptan can be dissolved in water, so every time you cut onions, you can put some water in the pot, and then put the chopping board in the water to cut onions, so that n-propyl mercaptan can be partially dissolved in water, which can reduce the irritation to human eyes.

Why can fruit sober up?

Excessive drinking is often a sign of drunkenness. Drunkenness is often accompanied by symptoms such as increased language, ineffective tongue, fever and numbness in cheeks, dizziness, and unstable standing ... These are all manifestations of drunkenness, and it is necessary to sober up.

Many people know that eating some sour fruit or drinking 1-2 clean vinegar can relieve hangover. What is the truth?

This is because fruits contain organic acids, for example, apples contain malic acid, oranges contain citric acid, and grapes contain tartaric acid. The main component of wine is ethanol, and organic acids can interact with ethanol to form esters to achieve the purpose of hangover.

Similarly, vinegar can relieve alcoholism because it contains 3-5% acetic acid, which can react with ethanol to produce ethyl acetate.

Although the fruit with sour taste and vinegar can alleviate the anesthetic effect of excessive ethanol, the effect is not ideal due to the interference of many factors in the above esterification reaction. Therefore, the best way to prevent drunkenness is not to drink too much.

Chemistry of soda water

In summer, people always like to drink soda. When you open the bottle cap, you will see boiling bubbles. Soon after drinking it, gas will come out, which will make you feel good. What kind of gas is this? This is carbon dioxide gas.

People often mix baking soda (sodium bicarbonate) and citric acid when making soda water. When baking soda and citric acid are mixed in water, they react to produce carbon dioxide gas, but the bottle has been blocked and carbon dioxide is forced to stay in the water. When the cork is opened, the external pressure is small, carbon dioxide gas escapes from the water, and bubbles can be seen churning. After drinking soda water, the temperature in the stomach is high, and the stomach has no time to absorb carbon dioxide, so it is discharged from the mouth.

Why should yellow rice wine be drunk while it is hot?

Yellow rice wine is made from grain through the interaction of distiller's yeast and medicinal liquor. Its main component is ethanol, but its concentration is very low.

Yellow rice wine also contains a very small amount of methanol, aldehydes, ethers and other organic substances, which have a certain impact on the human body. In order to minimize the residue of these substances, people generally blanch rice wine to about 60-70 degrees, because the boiling point of aldehydes, ethers and other organic substances is generally around 20-35 degrees, and even methanol is only 65 degrees, so these trace organic substances contained in rice wine are blanched. Therefore, drinking yellow wine while it is hot is good for health.

Frosted vegetables taste more delicious.

Vegetables contain starch, which is not only not sweet, but also insoluble in water. But after the first frost, the starch in Chinese cabbage changed from hydrolysis to maltase under the action of amylase in plants, and then into glucose under the action of maltose. Glucose is soluble in water and sweet, so green vegetables are sweet. So, why does this change occur in winter? That's because the starch in the vegetable plant turns into glucose and dissolves in water, and sugar is added to the cell fluid, so the cell fluid is not easy to be destroyed and the vegetable is not easy to be frozen. It can be seen that the sweetness of vegetables in winter is a phenomenon that vegetables themselves adapt to environmental changes and prevent freezing injury. In the first frost season, other vegetables, such as spinach, cabbage and radish, taste sweet, and so on.

What is the white powder on the outside of persimmon?

Fresh persimmons contain a lot of water, glucose and fructose. When it is dried into persimmon, the water gradually evaporates, and the glucose and fructose contained in the pulp penetrate into the epidermis. These two kinds of sugar have different properties. Fructose tastes sweet and absorbs water easily. When it permeates the surface of persimmon, it will catch the moisture in the air and attach to the epidermis of persimmon, similar to syrup and glucose outside the candied fruit. However, it is not easy to catch the moisture in the air. When it penetrates into the skin of persimmon, it becomes a layer of white powder, which just wraps the attached fructose and makes the whole persimmon dry. It turns out that this white powder is glucose powder.