Many Tea enthusiasts notice an issue when Drinking Tea: the infusion turns cloudy and less palatable once it cools down.

Why does this happen? Is drinking cooled tea harmful to one's health?

The substances that emit fragrance in tea are mostly high-boiling-point aromatic organic compounds, which can only volatilize into gases at high temperatures. Therefore, hot tea has a high-aromatic profile and better mouthfeel when freshly brewed.

If the tea cools down, the aroma, warmth, aftertaste, and character of the tea leaves lose their original flavors as the tea water cools.

When the temperature of the tea decreases, polyphenols and vitamins in the infusion are more prone to oxidation, leading to a gradual reduction in nutrient content. Prolonged exposure to air can also promote the growth of spoilage microorganisms, causing the tea to spoil and change flavor.

A tea infusion left to cool after being steeped at high temperatures is different from cold-brewed tea. Cold-brewed tea refers to tea made with cold boiled water, which causes minimal damage to nutrients in the infusion. The resulting cold-brewed tea has a unique taste and does not turn darker or become astringent or bitter; nor does it produce harmful substances.

Cold tea not only loses its flavor and aroma but may also support microbial growth, causing the tea to spoil and increase in harmful substances. It is therefore best to avoid drinking it.