Thickness is a quality that can be recognized by the general public and is one of the common traits of good tea.
Whether it's tea, liquor, or a bowl of slow-cooked soup, the appreciation for thickness is similar to our innate preference for sweetness—it arises from subconscious impulses and requires little training.
Thickness is not part of the basic taste sensations but rather a tactile sensation. A cup of tea contains many substances, but not all contribute to its thickness. If we simply consider the internal content, the Water-soluble solids should correspond to the described internal substances.
However, in reality, the content of water-soluble solids has little correlation with the thickness of the tea. In other words, some teas may have high water-soluble solid content but do not feel particularly thick.
This is not hard to explain, as the correlation between thickness and polyphenols is not significant.
For example, if we compare a strongly brewed spring Shoumei white tea made from Fuyun No. 6 with a normally brewed spring Shoumei white tea made from Dahao white tea, we find that even when the Fuyun No. 6 is brewed strong, it does not reach the thickness of the Dahao Spring Tea.
In terms of water-soluble solids, the strongly brewed white tea should contain more, but when tasting it, the tea feels both bitter and thin, lacking the full-bodied character of the spring tea.
It seems that polyphenols do not significantly contribute to the thickness of the tea, which makes it difficult to perceive the thickness. So what exactly influences thickness?
The substances that create the sensation of thickness are generally considered to be soluble sugars, including not only simple sugars like Glucose and fructose that impart a noticeable sweetness but also soluble pectins and starches.
These substances act to thicken the tea, creating a viscous texture. Besides soluble sugars, amino acids also play a supporting role, making the tea feel thicker.
Soluble sugars and amino acids appear in a cup of tea due to both Raw material factors and post-processing factors. Firstly, regarding raw materials, the presence of substances that contribute to thickness is primarily influenced by season and tree age.
Generally speaking, in the spring, the content of amino acids is relatively higher, while soluble sugars are more abundant in the fall. The older the tree, the greater the relative content of soluble sugars and amino acids in its leaves.
Therefore, overall, the sensation of “thickness” is more pronounced in spring teas, and the older the tree, the fuller the flavor of the tea. Different processing methods have varying effects on the thickness of the tea.
During withering and spreading out, due to the action of hydrolytic enzymes, the content of soluble sugars increases. During the process of killing green and withering, under the influence of temperature and humidity, hydrolytic enzymes accelerate their reactions, increasing the amount of soluble sugars.
During kneading, tea juice overflows, and the tea strands form with the help of these highly viscous soluble pectins. Some of these substances coat the outside of the tea strands, affecting the thickness of the tea because they increase the solubility rate of these viscous substances.
During the Fermentation of black tea and the pile-fermentation of dark tea under normal processing conditions, large amounts of soluble sugars are produced, enhancing the thickness of the tea. Therefore, under the same brewing conditions, black tea and Pu'er tea tend to be richer and smoother.
The sensation of thickness enhances the overall quality of the tea's flavor. This enhancement might occur through three mechanisms.
Firstly, substances that create thickness, such as soluble pectins, do not significantly affect taste since they have little flavor. What role do they play then?
These viscous substances adhere to our taste buds, creating a shielding effect. It's like using a neutral density filter in photography, which reduces the intensity of light. As a result, our perception of bitterness becomes more mellow.
When tasting pure polyphenols, the stimulation is like a direct collision with a metal hammer. However, when soluble pectins are added at the same concentration, it's like switching to a rubber hammer—the stimulating effect of the polyphenols is greatly softened.
Secondly, these highly viscous substances serve a lubricating function, easing the rupture of the lubricating film caused by the combination of polyphenols and salivary proteins, reducing our sensation of astringency. Astringency does not convey a sense of sophistication.
Lastly, these high-viscosity substances adhere to the walls of the mouth after swallowing the tea, along with some sugar, low-concentration polyphenols, amino acids, and aroma compounds, improving the quality and duration of the aftertaste.