This is because hot tea at higher temperatures has faster molecular movement, resulting in a more aromatic and flavorful brew—similar to how stir-fried vegetables release more fragrance when cooked in hot oil. Once the temperature drops, compounds like tea polyphenols and vitamins oxidize, gradually reducing their content. Tea left exposed to air for too long can also breed spoilage microorganisms, altering its taste and quality.

It’s common to observe that a bright orange-red tea turns yellowish-brown and cloudy over time. This is mainly due to caffeine forming complexes with catechins and their oxidation products as the temperature drops. However, these compounds are non-toxic and pose no health risks.

The aromatic compounds in tea are mostly high-boiling-point organic substances that volatilize at high temperatures, enhancing the tea’s aroma. Additionally, the initial fragrance, warmth, sweetness, and aftertaste of freshly brewed tea diminish as it cools.

Of course, tea that has been hot-brewed and left to cool is different from cold-brewed tea. Cold brewing involves steeping tea in cold water, which preserves nutrients and offers a distinct flavor without the cloudiness, bitterness, or harmful byproducts. Cooled tea, however, loses its aroma and taste and may harbor microorganisms that spoil it, increasing harmful substances. Therefore, it’s best to enjoy tea while it’s still warm.

Reprinted from: Tea Culture Bar