Firstly, one can distinguish between aged tea and new tea by its color. Green tea has a vibrant green color and a yellow-green, bright infusion; black tea has a lustrous black color and a bright red-orange infusion, which are signs of new tea. During storage, substances that contribute to the tea's color undergo slow decomposition or oxidation under the influence of light, air, and heat. For instance, the decomposition and oxidation of chlorophyll in green tea cause its color to become dull and grayish. The increase in theaflavins also makes the infusion yellowish-brown and unclear, losing its original fresh color. For black tea, prolonged storage leads to the oxidative condensation of tea polyphenols, which darkens the color. The increase in theaflavins also makes the infusion turbid and unclear, thus losing the fresh and vibrant character of new black tea.
Secondly, one can differentiate between new tea and aged tea by its aroma. Scientific analysis shows that there are over 300 aromatic compounds in tea, mainly alcohols, esters, and aldehydes. During storage, these compounds both continuously volatilize and undergo slow oxidation. Therefore, as time passes, the tea's aroma gradually becomes less intense.
Thirdly, one can also tell the difference between new tea and aged tea by its taste. This is because during storage, the taste-forming substances in tea, such as phenolic compounds, amino acids, and vitamins, either decompose and volatilize or condense into water-insoluble substances. This reduces the amount of effective taste substances that can dissolve in the tea infusion. Therefore, regardless of the type of tea, new tea generally has a mellow, fresh, and brisk taste, while aged tea tastes bland and lacks briskness.