Risks and Disadvantages of Drinking Overnight Tea

Whether you can drink overnight tea is still controversial. Some people think that overnight tea may produce carcinogens, while others say that overnight tea is actually good for your health.

In fact, overnight tea generally does not cause cancer, but the nutritional value and taste of overnight tea will decrease, and the aromatic substances in the soup will also volatilize. In addition, the heavy metals and pesticide residues in the overnight tea will increase, and because the tea is exposed to the air, it will produce a variety of harmful microorganisms and stimulate the stomach, which increases the risk of drinking tea soup.

Whether the tea is soaked in water for a long time or the tea soup is exposed to the air for a long time, the polyphenols will oxidize and cause the tea soup to change color, and the aromatic substances in the soup will also volatilize, resulting in a decrease in taste and loss of the original flavor of the tea soup.

No matter it is green tea, black tea, oolong tea, or Pu'er tea, etc., the tea polyphenols, catechins, and amino acids in the overnight tea will be reduced. In addition, the content of vitamin C and sugar substances will be greatly reduced, and the aromatic substances will also be reduced. Volatile, the overall nutritional value and taste are not as good as tea under normal brewing conditions.

From a health point of view, the content of heavy metals and pesticide residues in overnight tea increased significantly. The heavy metal leaching rate of overnight tea almost reached the maximum value! The more times the tea is steeped, the heavy metal leaching rate will decrease; the higher the temperature and the longer the soaking time, the heavy metal leaching rate will increase. When drinking tea, the leaching rate of pesticide residues does not necessarily increase with the increase of soaking time, but the possibility of increasing the amount of pesticide residues accumulated in tea soup is relatively high.

Although many pesticides are insoluble or difficult to dissolve in water, and as the water temperature decreases, the solubility in water will also decrease, but after long-term soaking, the accumulated pesticide residues will increase the risk of drinking.

Image Credit: Jason Goh

In addition, overnight tea will produce a variety of harmful microorganisms. When the tea is exposed to the air, most of the vitamins have been lost; while the protein, sugar, etc. soaked in the tea that has been left for a long time will provide nutrients for the reproduction of mold, bacteria, and other germs. The microbes of the tea soup sterilized by boiling water come from the air exposed to the outside world. In addition, the contact between the cup and the hands and mouth is also the main source of microorganisms. With the extension of soaking time, the number of microorganisms in the tea soup will increase greatly. The reproduction of microorganisms also has a great relationship with temperature. Most microorganisms are suitable for growth and reproduction at 28°C-30°C (82.4°F-86°F), especially in hot summer when tea tends to become sour and tasteless.

If left for more than 12 hours, it is best not to drink it, as it may cause diarrhea. A large amount of free tannic acid will be produced in overnight tea, which will directly stimulate the gastric mucosa. Regular drinking of overnight tea will greatly stimulate our stomach. It is worth mentioning that overnight tea stored in the refrigerator is more irritating to the stomach.

If you think it is wasteful to discard overnight tea, consider using it to wash your feet. The tannic acid in tea has bactericidal properties, particularly effective against filamentous bacteria that cause conditions like beriberi. Also, you can dry the steeped tea leaves and use them as mosquito repellent, which is both safe and fragrant. However, exercise caution and prioritize safety when igniting the dried tea leaves.