Some friends often say that green Tea is cold in nature and can harm the stomach. The stimulating effect of tea mainly comes from Caffeine and polyphenols in the leaves. When fresh tea leaves are processed into Black Tea and Green Tea, which one contains more caffeine and polyphenols?

Caffeine

Let's start with caffeine. The caffeine content in tea infusion is related to the tea-making process, raw materials, and brewing method. In terms of the manufacturing process, green tea undergoes a step called “kill-green,” where the temperature of the leaves will be very high instantly—the pot temperature for kill-green can be controlled, but it's hard to determine the leaf temperature, which is estimated to be above 120°C. Caffeine starts to sublimate at 120°C and sublimates significantly at 180°C. This means that some caffeine may disappear during the kill-green process.

In black tea production, there is no kill-green step, nor does it experience such high temperatures as during the kill-green process in green tea. If we take two identical fresh tea leaves and make one into green tea and the other into black tea, theoretically, the black tea should have a higher caffeine content, meaning black tea would be more stimulating than green tea.

In terms of raw material selection, high-quality green teas are typically made from young buds or young leaves, while black teas can be made from both young and mature leaves. The caffeine content in fresh tea leaves decreases as the maturity of the leaves increases—the young buds and first leaves have higher caffeine content, while mature leaves have lower caffeine content. Additionally, the caffeine content in the tea infusion is closely related to the brewing details. Therefore, it is impossible to make a general comparison regarding which has a higher caffeine content between black tea and green tea.

In fact, many people have measured the caffeine content in black and green tea infusions, and the results vary widely—a 240 ml cup of black tea may contain as low as tens of milligrams of caffeine or as high as sixty to seventy milligrams; the same applies to green tea. As for how much caffeine your cup of black tea or green tea contains, you would only know by actual measurement.

Polyphenols

Now let's talk about polyphenols. The polyphenol content in fresh tea leaves is related to the species of the tree. People judge whether fresh leaves are suitable for making green tea or black tea primarily based on the “polyamine ratio”—the ratio of polyphenols to amino acids, with a high ratio being suitable for black tea and a low ratio for green tea. It seems that black tea might have a higher polyphenol content. However, in reality, black tea production includes a step called “withering,” during which a significant portion of the polyphenols are oxidized into theaflavins and thearubigins, so the polyphenol content in black tea decreases during processing, but the extent of this decrease varies among different types of black tea.

The solubility of polyphenols in tea infusion is not affected by water temperature, while caffeine is relatively sensitive to water temperature. The lower the water temperature, the lower the solubility and slower the dissolution. Whether the caffeine and polyphenol contents in the tea infusion are well balanced is decisive for the bitterness or astringency of the tea.

The black tea production process is more complex than that of green tea, providing sufficient opportunity for caffeine and polyphenols to form complexes, so the two are more easily balanced in black tea infusion, leading to a less bitter and astringent taste.

It is more challenging to balance caffeine and polyphenols in green tea infusion, requiring certain techniques to control their dissolution rates. During brewing, green tea is generally brewed with water around 85°C, while black tea uses hotter water, also aiming to regulate the dissolution rates of the two substances.

However, water temperature is just one factor. Even high-quality green tea can easily become bitter if not brewed carefully, while lower-quality green tea can become both bitter and astringent. Perhaps this is why many people think that “green tea has a stronger stimulating effect.”