“Phenol-ammonia ratio” is a colloquial term referring to the ratio of total polyphenols to total amino acids in fresh leaves or finished tea. Polyphenols and amino acids are prominent representatives of carbon-containing and nitrogen-containing compounds in tea quality components. The ratio reflects the proportion of two primary quality components in tea and can largely determine the quality attributes of fresh leaves and the quality of the finished tea. Varieties suitable for Green Tea production require a low phenol-ammonia ratio; varieties suitable for Black Tea production require a high phenol-ammonia ratio; and varieties suitable for Oolong tea production require a moderate phenol-ammonia ratio. This ratio is also an important indicator of the taste intensity of the finished tea infusion.

Polyphenols

In tea infusions, catechins are the most abundant type of phenolic compound. Esters of catechins have a bitter and astringent taste and strong astringency. The astringency perceived when tasting tea is mainly due to the reaction between ester-type catechins and oral mucosal proteins, forming an impermeable substance that causes astringency. From a sensory perspective, astringency is also produced by stimulation of the tactile nerve endings. Simple catechins, on the other hand, primarily contribute to the refreshing sensation in the tea infusion. Research suggests that within a polyphenol content of 20% or less, taste scores are significantly positively correlated with polyphenol content. Within a polyphenol content range of 20-24%, the harmony of concentration, body, and freshness in the tea infusion is still maintained. When the polyphenol content increases further, although the concentration of the tea infusion increases, the freshness and body decrease, and the bitterness and astringency increase. Studies suggest that the correlation coefficient between the total amount of catechins and taste score is 0.929, EC (epicatechin) is 0.729, EGC (epigallocatechin) is 0.704, EGCG (epigallocatechin gallate) is 0.850, and ECG (epicatechin gallate) is 0.876. The impact of polyphenols on tea quality is complex. Due to their high content, they are the main determinant of the concentration of the tea infusion. It is not accurate to simply state a positive or negative correlation between polyphenols and the taste of the tea infusion; rather, it should be comprehensively analyzed from multiple perspectives, including the solubility of polyphenols, their absolute content, and the ratio to other taste-contributing substances, especially amino acids.

Amino Acids

Tieguanyin's taste is required to be mellow and fresh. Both the sweet and fresh sensations in the mouth are related to amino acids in the tea. There are many types of amino acids in tea, each with different characteristics. The highest content is Theanine, an amino acid unique to tea. Other amino acids present at higher levels include glutamic acid, aspartic acid, arginine, glutamine, and asparagine. In terms of taste characteristics, not all amino acids have a fresh taste; most are sweet. According to relevant reports, L-type amino acids are mostly bitter, some sweet or fresh, while D-type amino acids are all sweet. Amino acids that constitute proteins in nature are all L-type, so the amino acids obtained from protein hydrolysis in tea mostly impart a bitter taste to the tea infusion. The configuration of free amino acids in tea is difficult to determine, but it is certain that they do not solely contribute a fresh taste to the tea infusion but also bitterness and sweetness. These different tastes, after various combinations and interactions, form the various taste characteristics of the tea infusion, which is why some Tieguanyin teas we drink may initially be bitter but then have a sweet aftertaste.

Phenol-Ammonia Ratio and the Harmony of Taste in Tieguanyin Infusion

As mentioned earlier, polyphenols are one of the main substances in tea, imparting a bitter and astringent taste. Amino acids, on the other hand, are a prominent nitrogen-containing compound in tea quality components and are the main substances contributing to the freshness and aroma of Tieguanyin infusions.

Theoretically, the best scenario is when both polyphenol and amino acid contents are high and in a balanced ratio. Generally, the relationship between these two components is as follows:

1. High polyphenol content and high amino acid content result in a concentrated, fresh, and non-astringent taste.

2. Low polyphenol content and high amino acid content result in a mild, fresh, and non-astringent taste.

3. High polyphenol content and low amino acid content result in a concentrated, non-fresh, and bitter-astringent taste.

Did you get today's technical post?