The thinnest film that forms on the surface of strongly brewed tea is considered either a sign of good quality of the drink, or an indicator of the hardness and pollution of the water. To date, there is no unequivocal answer where the film on tea comes from - there are several versions explaining its origin.
Hard water?
Experts advise paying attention to the appearance of the film. The uniform color of the plaque or the smallest blotches in it indicate that too hard tap water has become the cause of the formation of the film. The high content of calcium carbonate in water, when combined with organic substances contained in tea, causes a film to appear. If you add a slice of lemon or a drop of lemon juice to the drink, the film will disappear.
There is also an opinion that the reason for the formation of a film is the oxidation of iron contained in water.
Rainbow in a cup
A thin rainbow film, homogeneous and easily broken when stirring the drink, is formed by essential oils and tannins contained in tea and giving it a unique aroma and tart taste. If the brewed tea is left untouched for some time, oils and tannins are oxidized - the result of this oxidation is a rainbow film on the surface of the liquid. The stronger the tea, the more noticeable it will be.
Another reason for the appearance of a brownish film, according to experts, is the oxidation of mineral and organic compounds, including caffeine and catechins, contained in tea, under the influence of oxygen in the air. The composition of this film is very complex - it includes protein compounds, purines, tannins, iron, calcium, and other substances and compounds.
Harmful or useful?
The opinions of experts on the effect of tea with film on human health differ. On the one hand, it is evidence of a high content of useful essential oils, on the other, it forms an insoluble coating, which, with constant use of strongly brewed tea, can settle on the mucous membrane of the stomach and intestines, interfere with the absorption of nutrients.
It has been found that drinking tea that has stood for a long time has the worst effect on human health - after brewing, black tea should be drunk for several hours, in no case leaving the tea leaves overnight. After that, the drink loses its beneficial properties, it increases the content of harmful substances, including toxic guanidine, formed during the oxidation of non-hazardous guanine contained in tea.
High concentrations of guanidine are extremely dangerous, and for the onset of symptoms of poisoning, it is enough to drink a few cups of yesterday's strong brew.
On the walls of the cups, due to the film, a badly washed off plaque forms, which sometimes even washing in the dishwasher does not help get rid of. If the tap water in your area contains a lot of calcium, magnesium and iron salts, it is better to get a special filter or use purified bottled drinking water for making tea. Do not forget that distilled water, as well as too hard, has no benefit to the body.
