When drinking tea, our sensitive tongues quickly convey the flavors of the tea broth to our brains, which can create feelings of satisfaction or enjoyment. But what exactly are the substances that our tongues taste?
The taste-contributing substances in tea broth can be summarized as follows: sugars, amino acids, phenolic compounds and their oxidation products (primarily catechins), purine alkaloids (mainly caffeine), organic acids, and tea saponins. Among these, catechins, amino acids, and caffeine have the greatest impact on the quality of tea. The taste of tea is a comprehensive response by our taste organs to the taste components present. Therefore, changes in the content and proportions of various taste components will affect the flavor of the tea broth.
Astringency — Phenolic Compounds and Their Oxidation Products
Catechins are the highest-content phenolic compounds in tea broth. Esters of catechins impart a bitter and astringent taste with strong astringency. The astringency experienced when drinking tea is primarily due to ester-type catechins reacting with oral mucosal proteins to form insoluble substances, causing a drying sensation. From a sensory perspective, astringency is also produced by stimulation of tactile nerve endings.
Bitterness — Purine Compounds (Primarily Caffeine)
Caffeine is the main taste-contributing purine compound in tea, imparting a bitter taste. Due to its volatility when heated, caffeine content decreases significantly over multiple infusions. Caffeine, with its ability to stimulate the central nervous system and activate brain cortex cells, as well as stimulate gastric and bile secretion, is one of the primary substances responsible for people's fondness for tea.
Cyanidins in tea broth are another source of bitterness. When cyanidin content exceeds its threshold in the tea broth, it imparts a noticeable bitterness. A concentration of 15 milligrams of cyanidin in 150 milliliters of tea broth produces a distinct bitterness. Purple buds contain 1% or more cyanidins. Summer teas, due to intense sunlight exposure, have high cyanidin content and many purple buds, which is why they tend to be more bitter and of lower quality.
Freshness — Amino Acids
The taste of green tea should be smooth and refreshing, and both the sweetness and the fresh, clean taste are related to amino acids in the tea. There are many types of amino acids in tea, each with different characteristics. The most abundant is theanine, an amino acid unique to tea. Other major amino acids in tea include glutamic acid, aspartic acid, arginine, glutamine, and asparagine. Not all amino acids impart a fresh taste; most are sweet or bitter.
According to reports, L-form amino acids mostly taste bitter, while a few taste sweet or fresh; D-form amino acids all taste sweet. In nature, the amino acids that make up proteins are L-form, so the amino acids obtained from protein hydrolysis in tea mostly contribute a bitter taste to the tea broth. Although it's difficult to determine the configuration of free amino acids in tea, it's certain that they don't just contribute a fresh taste but also bitterness and sweetness. These different tastes, combined in varying ratios and through their interactions, create the various taste profiles in tea broth.
Sweetness — Sugars and Other Substances
The sugars that impart sweetness in tea broth are primarily monosaccharides and disaccharides, which are soluble sugars in the tea. Although sugar content isn't particularly high, due to differences in taste thresholds and the locations of taste perception in humans, small amounts of sugar in tea can be perceived more strongly after a mild bitterness. This synergistic effect of sweetness and bitterness creates a pleasant experience when drinking tea. Soluble pectins and glycosides of phenolic compounds in tea broth also play a role in forming the taste. Water-soluble pectins give the tea broth a thick, smooth mouthfeel.
