Pay attention to these 5 points when eating pickled cabbage safely! Hardcore content is coming!

Recently, because the 3.15 Gala exposed the problems in pickling sauerkraut, many friends asked me whether kimchi is still safe to eat, and many friends also asked me to write about how to make sauerkraut safely.

Here I will briefly explain it in response to your request. I will first explain the scientific reasoning, and then summarize the key points of how to make and eat it. (For those who really don’t have the patience to read the scientific reasoning, please scroll down to the end of the article to read the suggestions.)

Foods such as pickles have been made since ancient times and are popular all over the world. If they are well made, they are safe and delicious. The lactic acid bacteria and lactic acid in them even have certain health benefits, helping to improve appetite, promote digestion, and improve intestinal health. However, if they are not well made, they may be contaminated with pathogenic bacteria, or the nitrite may exceed the standard, and even produce nitrosamine carcinogens.

Therefore, we must not simply condemn this type of food, but instead popularize knowledge about its rational production and supervise and inspect the safety and quality of related products.

Let me first explain the basic principle of making pickled cabbage. Once you understand the scientific principle, you will naturally know how to make it properly.

1 How do fresh vegetables become sour kimchi?

Before there were pure strains of bacteria or successfully made "kimchi water", vegetables were simply placed in a jar (or pond, or vegetable pit) and compacted. After a period of time, they became sour kimchi. This process is called "natural fermentation."

Where do the bacteria for natural fermentation come from? They are lactic acid bacteria that grow naturally on the surface of vegetables.

They use the small amount of sugar and amino acids in vegetable juice to produce lactic acid, which creates a sour taste.

Because these lactic acid bacteria cannot decompose large molecular proteins, safe sour kimchi tastes fragrant and has no odor.

They also cannot break down cellulose and pectin, so they do not damage the cell wall structure of vegetables. Therefore, successful kimchi has a crisp texture and is not sticky.

——What if there is a bad smell or it is sticky? That is the fault of bacteria. It means that the bacteria are not well suppressed during the fermentation process, and the safety is also worrying.

Of course, people in some areas just like to eat pickled vegetables that are a bit smelly. In fact, not every kind of bacteria can cause disease. Whether it is safe depends on luck. If the bacteria produce nitrosamines, although they are carcinogenic, they will not take effect after a few bites. It will take many years for its safety risk to show up.

2 How did lactic acid bacteria stand out?

After all, the raw vegetables have not been sterilized, and there are all kinds of bacteria on the surface, not just lactic acid bacteria. Why is lactic acid fermentation the final result? This is a good question.

Indeed, at the beginning, among the numerous kinds of fungi, lactic acid bacteria were not dominant at all.

After putting the vegetables in the jar or pool, they need to be compacted. This compaction has two important purposes. One is to squeeze out the air in the gaps, and the other is to squeeze out some of the vegetable juice. Especially after adding salt and then squeezing, the vegetable juice will come out easily.

These vegetable juices are nutritious. Although the sweetness of vegetables is not obvious, they also contain 2-5% soluble sugar. They also contain potassium, magnesium, multiple amino acids and vitamins. With such good food, various microorganisms will naturally flock to it and grow wildly.

Image source: Tuchong Creative

At this time, lactic acid bacteria did not have an advantage in the surging "bacteria tide". When you stand on tiptoe and take a look, you will find that there are too many microorganisms at the top... Especially those bacteria that like oxygen, because aerobic oxidation produces more energy, and their growth rate is also very fast.

However, lactic acid bacteria are patient.

This is because the vegetables are pressed very tightly, leaving little air, and the top is sealed, so oxygen cannot enter, so the oxygen is quickly used up. The fungi that grew rapidly at the beginning gradually felt "lack of oxygen", could not reproduce, and became weak.

What to do if there is no oxygen? Anaerobic fermentation is needed. This is what lactic acid bacteria are good at. It ferments glucose into lactic acid and releases a little energy. Because lactic acid fermentation produces less energy, the lactic acid bacteria proliferates more slowly.

In fact, some bacteria can produce acid, but their ability to tolerate acid is not as good as that of lactic acid bacteria. As the acid in the jar becomes more and more acidic, the oxygen is gradually depleted, and most of the bacteria feel that they "can't survive" and are gradually suppressed, and most of them die.

In this way, after a few days or even more than ten days, the lactic acid bacteria finally came from behind and became the most dominant bacteria in the kimchi jar.

At this time, we can breathe a sigh of relief, because after the lactic acid bacteria take over, the pickled cabbage is safe.

What if there is always oxygen? That would be a problem. The bacteria would be active all the time and the food would be unsafe. Therefore, the food should be covered with water and not exposed to the air. The edges of the kimchi jar must be sealed with water! This is a key measure to prevent oxygen from entering!

3 Why does qualified kimchi not contain much nitrite?

As mentioned earlier, at the beginning, there is a lot of oxygen and sufficient nutrition, and various bacteria proliferate wildly. This is actually very unsafe. Because many bacteria can produce "nitrate reductase", which will cause the nitrite content in the vegetables to rise rapidly, resulting in a "nitrite peak". This nitrite peak is relatively consistent with the activity of bacteria such as Enterobacteriaceae (Yan Pingmei et al., 2010).

The time period when the bacteria are most active is usually between 2 and 8 days after the start of production, depending on factors such as vegetable variety, fermentation temperature, salt content, and other ingredients.

However, the duration of the "nitrite peak" is not long. As oxygen is depleted and acidity rises, these bacteria will gradually decline. And "good bacteria" such as lactic acid bacteria do not produce nitrite. Therefore, when lactic acid bacteria become popular, the production of nitrite will be negligible.

But what about the nitrites that have already formed? The answer is: under acidic conditions, especially when the pH value is below 4, the nitrites that have already formed will continue to decompose. The stronger the acidity, the faster the decomposition, so the content becomes lower and lower. At the same time, lactic acid bacteria themselves contain "nitrite reductase", which will also reduce the nitrite content. Finally, it will be reduced to a safe level that is completely harmless to health. It is usually safe to leave it for about 14 days, and in winter, you can wait until 20 days for safety reasons.

In short, as long as the kimchi is sour enough and contains lactic acid bacteria, we don’t need to worry about the nitrite problem.

4 When making pickles, sauerkraut, and kimchi, what can be added to reduce nitrite?

Studies have shown that adding ingredients such as vitamin C, garlic, onions, ginger, fresh peppers, or adding antioxidants such as flavonoids when making kimchi can effectively reduce the amount of nitrite produced during the fermentation process.

In fact, as mentioned before, if you wait patiently for more than ten days, the nitrite content will decrease by itself when the acidity is high enough. However, some people are very impatient and want to eat it after pickling/soaking for a few days. This is when the nitrite content is the highest, which is very dangerous. Therefore, it is very important to add some ingredients that inhibit nitrite.

For example, the pickling time of Korean kimchi is very short, but a large amount of mashed garlic, chili peppers and fruits are added to it, which can effectively inhibit the activity of miscellaneous bacteria and improve the safety of the product.

5 What can be eaten with pickled cabbage to reduce nitrite?

Studies have found that even if you are not sure about the product itself, eating some foods rich in vitamin C or taking vitamin C tablets with meals can effectively reduce the amount of nitrite absorbed by the human body.

This is because vitamin C is a reducing agent, while nitrite is a strong oxidizing agent. When the two meet, a redox reaction will occur, turning nitrite into nitric oxide and nitrogen gas.

Experiments have confirmed that adding vitamin C to kimchi products can greatly reduce the content of nitrite (Gao Yurong, 2010). Other studies have found that under simulated gastric fluid conditions, after adding vitamin C, the concentration of nitrite gradually decreases over time, and up to nearly 90% of nitrite can be eliminated (Zhan Xiuhuan et al., 2016).

So, when it comes to the food safety of kimchi, it is enough to remember these few points.

1 When buying pickled vegetables, choose those with a fragrant taste and a crispy texture, which are safer.

2 When making homemade sauerkraut, be sure to isolate it from oxygen and seal the jar tightly to give the lactic acid bacteria a chance to become dominant.

3 Don’t be impatient when making it. Wait a few days and wait until the nitrite peak has passed before opening and eating it.

4. Add ingredients such as onion, ginger, garlic, chili, pepper or vitamin C during the preparation process to reduce the amount of nitrite produced.

5 If you are worried, you can eat kimchi with vegetables and fruits rich in vitamin C.

Finally, I would like to remind you that sauerkraut and kimchi are suitable for people with poor appetite, indigestion, anemia, calcium deficiency, etc. 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 too much sauerkraut and kimchi.

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Source: Fan Zhihong_Original Nutrition Information