Can overnight tea be drunk? After testing 3 types of overnight tea, I finally figured it out.

For tea lovers, the most embarrassing thing is that they make too much tea and cannot finish it.

Let it sit until the next day. There are many sayings online that you shouldn't drink overnight tea:

Some people say it contains a lot of bacteria and drinking it will cause diarrhea;

Some people say that it will breed a lot of nitrite, and drinking it for a long time will cause cancer;

Some people also say that after being left overnight, one of the most important nutrients in tea (tea polyphenols) will be oxidized and decomposed. In this case, drinking overnight tea is worse than drinking boiled water.

So can we still drink overnight tea happily?

In order to answer everyone's questions, we actually brewed three pots of tea, left them overnight devoutly, and sent them to the laboratory to measure the various indicators that everyone was concerned about.

Taking into account the different tastes of tea, we chose three typical teas: green tea (Longjing tea), black tea (Qimen black tea) and oolong tea (Anxi Tieguanyin).

In order to be as close as possible to the situation of some particular tea drinkers, our technician sister specially checked the brewing conditions of different teas. The brewing conditions of the three kinds of tea this time are as follows:

We filtered out the brewed tea leaves, took out some blank samples, and sent them directly to the laboratory on the same day.

Because everyone has a different definition of overnight tea, we can only count the first case with the longest interval (from the previous night to the next night) as overnight tea. If there is no problem with tea with an interval of 24 hours, then everyone can drink overnight tea without worry.

We gave the remaining tea to three colleagues (to drink directly), then left it open on the desk overnight and took overnight samples the next day (24 hours later).

Then it was sent to the laboratory to test the total colony count, nitrate/nitrite content, and changes in tea polyphenols content in the tea soup.

Sample fee 292.26 + testing fee 5328 = 5620.26 yuan

Is overnight tea hygienic? Can we drink it? Let's take a look at the test results below.

1. Is overnight tea hygienic? In order to verify the hygienic condition of overnight tea, we measured the total number of colonies in three overnight tea samples.

The test results are as follows:

The total colony counts of all overnight teas were less than 10 CFU/mL.

What does this mean? The limit requirement for the total colony count in drinking water in GB 5749-2006 Drinking Water Hygiene Standard is less than 100 CFU/mL, and the total colony count in overnight tea is much lower than this limit.

It seems that whether it is overnight green tea, black tea or oolong tea, the hygiene conditions are good. Those who are worried can rest assured.

2. Will the tea polyphenols in overnight tea be reduced? Tea polyphenols are a very important nutrient in tea. They can resist oxidation, inhibit bacteria, and lower blood sugar and blood lipids. The biggest contributor to the various benefits of drinking tea is the tea polyphenols in tea.

Among the three types of tea, green tea contains more tea polyphenols. If tea polyphenols are decomposed after being stored for a long time, the performance of green tea should be the most obvious.

We tested the changes in tea polyphenol content in overnight green tea:

Judging from the results, the tea polyphenol content of overnight green tea is almost the same as that of freshly brewed tea, and has not been decomposed to a large extent.

Tea polyphenols are a broad-spectrum antibacterial agent that can not only inhibit bacteria but also kill bacteria. A bold guess is that it may be because of the presence of tea polyphenols that tea does not breed too many bacteria after being left overnight.

Even green tea with a high content of tea polyphenols does not have much change in its tea polyphenol content after being left overnight. Friends who are worried about the loss of nutrients can rest assured.

3. Does overnight tea cause cancer? The cancer risk is mainly related to the nitrate and nitrite content in tea.

We have mentioned these two substances many times. They are classified as Class 2A carcinogens by the International Agency for Research on Cancer (IARC), which means "probably carcinogenic."

If the nitrate and nitrite in overnight tea really increase, you should never drink it.

We tested the changes in nitrate and nitrite in 3 types of tea before and after overnight storage. The results are as follows:

According to the test results, there was no significant change in the nitrate and nitrite levels of the three teas after being left overnight.

Even if you drink ten cups of overnight green tea, which has the highest nitrite content, the amount you intake is less than that of a plate of overnight stir-fried vegetables (at room temperature).

How much nitrite is in leftover food? Click here to check: Can leftover food be eaten? Let the actual test data tell you

Instead of worrying that overnight tea may cause cancer, it is better to eat less bacon and cured meat, and less vegetables that have been left at room temperature overnight.

Is overnight tea safe to drink? According to our test results, it is safe to drink.

In fact, sometimes, as long as we think about it carefully, some rumors will be self-defeating. If overnight tea is really not drinkable, then who would sell the tea drinks that have been left for who knows how many days and nights?

However, we also want to remind everyone that this test is based on the situation within 24 hours. If you are a warrior and can keep the tea for longer, it is best not to drink it.

After all, tea that has been left for too long is not only prone to dust and insects flying into it, but it may not taste very good.

When you taste tea, what you want is the taste of the freshly brewed tea.

Do you have friends who love to drink overnight tea? Please forward this answer to them, and they can drink tea without worries in the future!

By the way, I heard that cold brewed tea is very popular now. Do you think this kind of overnight tea brewed with cold water is drinkable? Welcome to the comment section to chat.

References: [1] Wang Juan, Pei Yinghong, Cheng Lijia, et al. Research progress on the antibacterial effect of tea polyphenols and its development prospects as a natural mildew inhibitor [J]. Chinese Food Additives, 2020, 31(11): 130-138.

[2] Zheng Qingmei, Chen Kunping, Zhong Yanmei, et al. Determination and analysis of the main components of four types of tea and their tea residues [J]. Guangdong Agricultural Sciences, 2015(06):14-20.