Friends who love drinking Dancong tea often notice a slight bitterness in the process of enjoying it. Consequently, some Dancong tea drinkers believe that such Dancong tea leaves are not of good quality. In fact, not all bitterness in Dancong tea is undesirable. Whether it is good Dancong tea depends on whether the bitterness is followed by a sweet aftertaste. "We cannot simply judge the quality of Dancong tea leaves based on whether the tea soup has a sweet aftertaste," explained a Dancong tea professor. "The flavor of Dancong tea soup is determined by the comprehensive reaction of our taste senses to the flavor compounds present in the tea leaves. Different Dancong teas exhibit different flavors due to variations in the types, contents, and proportions of their flavor components."

1. Main Flavor Compounds in Dancong Tea Soup

In reality, the taste of Dancong tea is a harmonious blend of multiple flavors. The primary flavor compounds in Dancong tea include tea polyphenols and their oxidation products (such as theaflavins, thearubigins, etc.), amino acids, caffeine, soluble sugars, organic acids, water-soluble proteins, and aromatic oils. Differences and changes in the types, contents, and ratios of these substances across various Dancong tea categories profoundly influence the taste of the tea soup. The four main flavors of Dancong tea soup and their corresponding compounds are illustrated below:

Flavor Components in Dancong Tea Soup

Polyphenol content is high in fresh Dancong tea leaves, generally ranging from 18% to 36% (dry weight). Most polyphenolic compounds have a bitter and astringent taste. Due to their high content and predominant proportion among water-soluble extracts, they are the main substances determining the taste of Dancong tea soup.

Caffeine has a bitter taste. In Dancong tea soup, caffeine forms complexes with a large amount of catechins, theaflavins, or thearubigins. This complexation prevents binding with proteins, altering the flavor characteristics. This change contributes to the formation of a fresh and mellow taste in the tea soup while reducing bitterness and astringency.

Amino acids are the main substances contributing to the fresh and refreshing taste of tea. Dancong tea contains a rich variety of amino acids, each with different flavor properties. For example, theanine, which accounts for 50%-70% of the total amino acids in tea, has a particularly high refreshing taste. It can mitigate the bitterness and astringency of the tea and enhance its sweetness. Glutamic acid, glycine, proline, etc., coexist with theanine in the tea soup and have a synergistic effect on presenting theanine's umami flavor.

The sweet taste in Dancong tea soup mainly comes from soluble sugars such as monosaccharides and disaccharides present in the tea leaves. They help mask and balance the bitter and astringent tastes to some extent. The higher their content, the more mellow and less bitter the tea taste becomes. Some amino acids, catechins, and thearubigins also contribute to the sweetness of the tea soup. Yunzixuan Pu'er Dancong Tea.

2. What is "Hui Gan" (Sweet Aftertaste)?

"Hui Gan" is a common natural sensory effect when drinking tea and a positive evaluation of the flavor of high-quality tea leaves. The "hui gan" effect is primarily formed by the combined action of bitter/astringent and sweet tastes, creating a specific flavor profile. It is characterized by a slight initial sweetness with mild bitterness, a relatively long aftertaste in the mouth, and a gradual dominance of sweetness over bitterness over time, ultimately ending with a sweet note. The sensory experience is mainly described as: "slightly bitter upon entry, with a clear sweetness in the aftertaste," or "initially bitter with a hint of sweetness, followed by diminishing bitterness and growing sweetness, with the sweet aftertaste lasting longer than the bitter sensation."

However, not all plants possess both these tastes simultaneously. For instance, bitter gourd and lotus seeds are bitter without sweetness, while licorice is sweet without bitterness. The production of the "hui gan" taste in tea soup usually requires bitterness as a prerequisite, with sweetness emerging after the bitterness. Good tea often exhibits "hui gan," and the intensity and persistence of this aftertaste are also considered indicators of tea quality. Compared to an immediately apparent sweetness upon entry, this "sweetness after bitterness" transformation is more dramatic and is more frequently associated with the quality of good tea.

3. What Causes "Hui Gan" in Dancong Tea Soup?

One theory suggests it is the result of the transformation of astringency. Professor Wang Yuefei, Deputy Director of the Tea Science Department at Zhejiang University, expressed his view in his edited book "Tea Culture and Tea Health": "Tea contains tea polyphenols, which can bind with proteins to form an impermeable film in the oral cavity. The contraction of local oral muscles caused by this film creates an astringent sensation, making us perceive the initial bitterness of the tea. If the tea polyphenol content is appropriate, forming a film of only one or two molecular layers, this film is of moderate thickness. Initially, there is an astringent feeling in the mouth. Shortly after, as the film ruptures and the local oral muscles begin to recover, the astringency transforms, presenting the sensation of 'hui gan' and saliva production." Therefore, Professor Wang Yuefei believes that "hui gan" is the result of the binding between tea polyphenols and proteins.

Another theory posits that "hui gan" is an oral illusion, namely a "contrast effect." In their 1979 paper "Relationships between Different Taste Qualities and Stimuli," Professors McBurney and Bartoshuk proposed: "Sweetness and bitterness are relative concepts. After tasting sweeteners like sucrose, you will find water tastes somewhat bitter. Conversely, after tasting bitter substances like caffeine and quinine, you will perceive water as sweet." This phenomenon is a contrast effect, leading many to believe this illusion might also be a factor contributing to "hui gan."

However, a stronger bitterness in the tea soup does not necessarily mean a more intense "hui gan." Some teas present bitterness without the awaited sweet aftertaste. Others may not be very bitter or astringent initially but exhibit a pronounced and persistent "hui gan." Regarding the mechanism of "hui gan," academic research is ongoing systematically and in-depth, with no absolute conclusion yet. However, some scholars' research and viewpoints can serve as references.

However, experiments by many scholars and experts have identified some components in tea soup that might cause "hui gan":

1. Tea Polyphenols and Total Sugar: Xu Yongquan et al. used an electronic tongue (an intelligent recognition electronic system mimicking the human taste mechanism) to analyze the taste of tea soup. The study showed a significant positive correlation between the bitterness of tea soup and the "hui gan" taste, indicating they complement each other. There was also a significant positive correlation between the content of tea polyphenols/total sugar and the intensity of the "hui gan" taste, suggesting that within a certain concentration range, both tea polyphenols and total sugar help enhance the "hui gan" intensity. For example, raw Pu'er tea generally has high tea polyphenol content and noticeable "hui gan," which corroborates this point.

2. Flavonoids: Although there are no reports in the tea industry stating flavonoids can produce "hui gan," there are reports that flavonoids are the substances causing "hui gan" in olives. The bitterness of olives comes from special chemical components like oleuropein, flavonoids, and polyphenols, with flavonoid content being higher than in other foods. The bitter substances in bitter gourd are momordicosides and charantin; in Kuding tea, they are glycosides and a small amount of flavonoids. Glycosides only exhibit bitterness, so eating bitter gourd feels only bitter with almost no "hui gan." The taste perception of flavonoids is very peculiar: initially bitter and astringent, but after a while, a natural sweetness can be felt. The flavonoids in olives are the main reason for their "hui gan," and higher flavonoid content leads to more pronounced "hui gan" and a mellower aroma. The flavonoid content in tea leaves is about 3%-4% of the dry matter. However, the mechanism of flavonoids causing "hui gan" is still under research and not entirely clear.

3. Organic Acids: Organic acids in tea stimulate the salivary glands to secrete, producing the sensation of "saliva production and sweet aftertaste." Tea contains various organic acids, accounting for about 3% of the total dry matter. Most organic acids in tea are free organic acids, such as malic acid, citric acid, succinic acid, and oxalic acid. Other organic acids are formed during tea processing. The content of organic acids increases during the withering and oxidation processes of tea leaves. Therefore, drinking oolong teas like Dancong makes it easier to feel a persistent "hui gan," while properly spread green teas can also exhibit a certain degree of "hui gan."

4. Polysaccharides: Tea soup contains polysaccharides, which themselves are not sweet but have a certain viscosity, causing them to linger in the mouth. Saliva contains salivary amylase, which can catalyze the hydrolysis of starch into maltose, a sweet sugar. The enzymatic breakdown of polysaccharides requires time, and this time difference creates the perception of "hui gan."

5. Many tea drinkers always show a fondness for the "sweetness" in tea. Terms like "mellow and sweet," "sweet," and "hui gan" are often used to describe the quality of high-grade teas. In terms of drinking pleasure, a mellow, fresh, and non-bitter/astringent tea flavor is most likely to evoke pleasant emotions. However, for many seasoned tea lovers, tea that can achieve "sweetness after bitterness" is truly good tea. Although the mechanism behind "hui gan" remains unclear, it does not hinder our pursuit of "sweetness after bitterness" while savoring tea—because tea is also like life.