Many have noticed that if you leave brewed tea for a while, a film forms on its surface. It has a pearly hue and shimmers with all the colors of the rainbow. Why does this film form? There are several theories, although none of them have been officially confirmed. Some believe that the culprit is overly hard water. Others are inclined to believe that the film forms as a result of the interaction of chemical elements found in tea with oxygen. Let’s try to figure out how objective these assumptions are. We should also find out if this layer is dangerous for the human body.
The Effect of Water Composition on Tea Film
It is necessary to carefully select water for brewing tea. Why? Ordinary tap water has high hardness and contains a large amount of iron and other impurities. After brewing with such water, a coating in the form of a film can very quickly form on the surface of the tea. After a few hours, the film becomes oily and more noticeable. It contains tea essential oils with impurities.
What kind of water is best for brewing and why? The best option is spring water, but finding such a source and using it constantly is very difficult. Bottled drinking water, which can be purchased at any supermarket, is more accessible. Distilled water will also work, as long as it is oxygenated. When brewing with good water, the layer on the tea will be practically invisible or there will be no film on the tea at all.
The Effect of Tea’s Chemical Composition on the Film
Tea leaf extract is a complex chemical compound. It includes catechins, theaflavins, thearubigins, caffeine alkaloids, proteins, mineral salts, and other substances. Many of them, when interacting with air, form a mixture of oxidation products and condensate, osmolize, forming a film. In ready-made tea, caffeine is present in two states: in combination with tannin and in a free state. Its compound with tannin (tannin caffeine) is responsible for the formation of the film.
It is believed that in black tea, the maximum caffeine content is reached after only five minutes. Therefore, longer brewing is not recommended. Studies have shown that the formed layer contains derivatives of catechins, nitrogenous bases, protein molecules, calcium, iron, and magnesium.
Tea Film: A Hidden Danger
The Chinese, who know a lot about good tea, believe that tea brewed the day before becomes poison by morning. The Japanese also share this opinion. Of course, the film on tea cannot cause poisoning. But it contains a large amount of oxidized low-molecular tannins, derivatives of catechins, nitrogenous bases, protein molecules, calcium, iron, and magnesium. If an insoluble film enters the human body, it can cause severe irritation of the mucous membrane of the intestines and stomach.
The film, covering the mucosa, prevents the absorption of nutrients. Intestinal peristalsis slows down, and food masses accumulate in the gastrointestinal cavity over time. This leads to putrefactive and fermentation processes. Bacterial activity increases, erosion may develop, and ulcers may appear. In the presence of diseases such as duodenitis, gastritis, it is better to refrain from regular consumption of tea with a film, so as not to provoke an exacerbation of the disease.
The most dangerous tea is the one that has been brewed for more than 12 hours. In it, guanine, purine compounds that are found in tea along with caffeine, accumulate in large doses. The oxidation product of guanine – guanidine, appears in tea 15 minutes after brewing or when boiling brewed tea. Guanidine is a toxic substance that causes an increase in pressure and accelerates the heartbeat. An overdose of this substance is dangerous.
How to Prevent Film Formation
To prevent the formation of a tea film, which can negatively affect the human body, or to reduce this effect, you need to follow simple rules.
When brewing, it is necessary to use soft water, spring or bottled. Brew tea according to the rules. It is not recommended to brew tea for more than 15 minutes. Do not drink yesterday’s tea on which a film has already begun to form.