You should refuse “yesterday’s” tea not only because you won’t be able to taste and aroma the tea. If the drink is left for several hours in the open air, bacteria, and harmful compounds begin to form in it under the influence of oxygen.
The proof that the tea should not be drunk is a thin OXIDE film on the surface of the tea.
It appears as a result of the oxidation of organic substances contained in tea by oxygen. They include protein molecules, iron, magnesium, calcium, nitrogenous bases (theophylline, caffeine, guanine), etc. The film leaves a coating on the cup.
These substances are most destructive to the organs of the gastrointestinal tract, mainly the liver.
But what should someone who does not like to drink hot tea do? They should drink it warm, 10-15 minutes after brewing.
Green tea, tea with karkade, and any other herbs are served cold, and cooled black tea do the body only harm.
If several hours or even days have passed since brewing, such a drink becomes very toxic.