Recently, because the "March 15 party" exposed the problems in pickled vegetables, many friends worried about whether pickles can be eaten safely. In fact, sour pickles, if prepared, are safe and delicious. The lactic acid bacteria and lactic acid contained in them are even beneficial to health. They can help improve appetite, promote digestion and protect intestinal health; If it is not done well, it may pollute pathogenic bacteria, or nitrite exceeds the standard, and even produce nitrosamine carcinogens. Therefore, for such a kind of food, we must not "kill with one stick", but popularize the knowledge of reasonable production and strengthen the supervision of the safety and quality of relevant products. This article will introduce the basic principle of making sour kimchi, because if you understand the scientific principle, you will naturally know how to make and eat reasonably. How do fresh vegetables turn into pickles? Safe sour kimchi has fragrance and no odor Before there is no pure strain or successfully made kimchi water, put the vegetables directly into the jar (or pool or vegetable pit) and compact them. After being stuffy for a period of time, they become sour kimchi. This process is called "natural fermentation". Where do naturally fermented bacteria come from? They are lactic acid bacteria on the surface of vegetables. They use a small amount of sugar and amino acids in vegetable juice to produce lactic acid, which also produces sour taste. Because these lactic acid bacteria can not decompose macromolecular proteins, the safe sour kimchi tastes fragrant and has no odor. They also can't break down cellulose and pectin, so the successful kimchi is crisp and has no sticky feeling. What if it's soft or sticky? That's the bad thing that miscellaneous bacteria do, which shows that miscellaneous bacteria are not well inhibited in the fermentation process, and the safety is also worrying. Of course, people in some areas "like that mouth" and like to eat a little smelly pickles. In fact, not every kind of miscellaneous bacteria is pathogenic. Whether it is safe depends on luck. If nitrosamines are produced by the action of miscellaneous bacteria, although they cause cancer, they will not work after a few bites, and it will take many years to show its safety risk. Lactic acid bacteria are good at anaerobic fermentation It's "superior" sour pickles are safe In other words, the vegetable raw materials have not been disinfected. There are all kinds of miscellaneous bacteria on the surface. Isn't it only lactic acid bacteria? Why does lactic acid fermentation last? This is a good question. Indeed, at the beginning, lactic acid bacteria did not dominate among all kinds of fungi in Wuyang. After putting the vegetables into the jar or pool, they should be compacted. This compaction has two important meanings: one is to squeeze out the air in the gap, the other is to squeeze out the vegetable juice a little, especially after adding salt, the vegetable juice is easy to come out. These vegetable juices are nutritious. Although the sweetness of vegetables is not obvious, they also contain 2% - 5% soluble sugar, including potassium, magnesium, a variety of amino acids, vitamins and other nutrients. With such good food, of course, all kinds of microorganisms rush forward and grow crazily. At this time, lactic acid bacteria are not dominant in the surging tide of bacteria. It "stands on tiptoe" to see that there are too many microorganisms in the top... Especially those that like oxygen. Because there is more energy generated during aerobic oxidation, they grow very fast. But lactic acid bacteria are patient. The food was really pressed. There was not much air left. The top was sealed again. Oxygen could not enter, so the oxygen ran out quickly. Those miscellaneous bacteria that grew rapidly at the beginning slowly felt that "hypoxia" could not proliferate and that their successors were weak. What if there's no oxygen? Anaerobic fermentation is needed, which is what lactic acid bacteria are good at. It ferments glucose into lactic acid, releasing a little energy. Because lactic acid fermentation produces less energy, the proliferation rate of lactic acid bacteria is relatively slow. In fact, some of the miscellaneous bacteria can produce acid, but their ability to tolerate acid is no better than that of lactic acid bacteria. As the jar became more and more sour and the oxygen gradually ran out, the vast majority of miscellaneous bacteria felt "simply unable to live", so they were gradually inhibited, and most of them even died. In this way, after a few days or even more, lactic acid bacteria finally came from behind and became the most dominant bacteria in the pickle jar. At this time, we were relieved. Because after lactic acid bacteria "up", sour kimchi is safe. What if there's always oxygen? That's trouble. If miscellaneous bacteria are always busy, the food is not safe. Therefore, the vegetables should be covered with water and not exposed to the air. The edge of the pickle jar must be sealed with water, which is the key measure to avoid the entry of oxygen. Pickles that have just begun to be pickled are the least safe Nitrite can only be decomposed after 14 days As mentioned earlier, at the beginning, there was plenty of oxygen and nutrition, and all kinds of miscellaneous bacteria proliferated wildly. At this time, it was actually very unsafe. Because many miscellaneous bacteria can produce "nitrate reductase", the nitrite content in the dish will rise rapidly and a "nitrite peak" will appear. The time range of vigorous miscellaneous bacteria activities is usually within 2-8 days after the start of production, depending on vegetable varieties, fermentation temperature, salt content and other ingredients. However, the duration of "nitrite peak" is not long. As oxygen runs out and acidity rises, these bacteria will gradually decline. These "good bacteria" of lactic acid bacteria will not produce nitrite. Therefore, when lactic acid bacteria become the climate, nitrite production will be very small. But what about the nitrite that has formed? The answer is: under acidic conditions, especially below pH 4, the formed nitrite will continue to decompose. The stronger the acidity, the faster the decomposition, so the content is lower and lower. At the same time, lactic acid bacteria contain "nitrite reductase", which will also reduce the content of nitrite. Finally, it will be reduced to a completely harmless and safe level. It's usually safe in about 14 days. In winter, it can wait for 20 days to be safe. In short, as long as pickles are sour enough and lactic acid bacteria dominate the world, we don't need to worry about nitrite. When making pickles, pickles and pickles What can be added to reduce nitrite? Research shows that adding vitamin C, garlic, onion, ginger, fresh pepper and other ingredients, or adding antioxidant substances such as flavonoids can effectively reduce the amount of nitrite produced in the fermentation process. In fact, the above also said that if you wait patiently for more than ten days, after the acidity is high enough, the nitrite content will be reduced by yourself. However, some people are very impatient and want to eat after pickling / soaking for a few days. At this time, the nitrite content is the highest, which is very dangerous. Therefore, it is important to add some ingredients to inhibit nitrite. For example, the pickling time of Korean kimchi is very short, but a large amount of garlic paste, pepper and fruit are added, which can effectively inhibit the activity of miscellaneous bacteria and improve the safety of food. When eating sour pickles What can be more reassuring to eat with? If you are still worried about the product itself, when you eat with some foods rich in vitamin C or vitamin C tablets, it will also effectively reduce the amount of nitrite absorbed by the human body. This is because vitamin C is a reducing agent, while nitrite has strong oxidation. When the two meet, redox reaction will occur, turning nitrite into nitric oxide and nitrogen. To sum up, it is enough to remember the following items about the food safety of sour pickles: 1. When buying sour kimchi, choose one with fragrant taste and crisp texture, which is relatively safe. 2. When making sour pickles, be sure to isolate oxygen and seal the jar so that lactic acid bacteria can become the mainstream. 3. Don't be impatient when doing it. Wait a few more days and open it for consumption after the nitrite peak has passed. 4. Add ingredients such as onion, ginger, garlic, pepper, pepper or vitamin C to reduce the production of nitrite. 5. If you don't feel at ease, you can eat pickles with vegetables and fruits rich in vitamin C. Finally, I would like to remind you that pickles and pickles are suitable for people with loss of appetite, dyspepsia, anemia and calcium deficiency. Lactic acid itself is conducive to the absorption of calcium, iron, zinc and other minerals. However, people with excessive stomach acid and gastroesophageal reflux are not suitable for eating more pickles and pickles. (outlook new era)