Bitterness of tea

Some foodstuffs have a bitter taste. A certain degree of bitterness is sometimes desired by the consumer and regarded as a typical flavor note (e.g., in grapefruit, cocoa, coffee, beer, tonic water, tea).

Bitterness of foodstuff may be caused either by naturally occurring bittering compounds or by chemical during storage or processing. The bitterness and astringency of tea are mainly formed by the combination of tea polyphenols, caffeine, and some amino acids.

Catechins account for approximately 70%-80% of total tea polyphenols. The main polyphenols found in tea are flavonoids. Flavonoids are a group of bioactive compounds synthesized during plant metabolism. Flavonoids contain two six-carbon rings linked by a three-carbon unit, which is also known as a chalcone structure.

Catechins (also referred to as flavanols) are bioactive compounds that are a subclass of flavonoids, and, in tea, are the main secondary metabolites. The four components in tea with the highest catechin content are epicatechin (EC), epicatechin gallate (ECg), epigallocatechin (EGC), and epigallocatechin gallate (EGCg). According to recent studies sensory evaluations indicated that the taste of catechin is bitter and astringent.

Green teas or teas made with tea leaves harvested later in the season have less theanine but more catechins and, therefore, have more astringency and bitterness. Thus, green teas or teas made with leaves harvested early in the season may have umami and sweet taste whereas green teas made with leaves harvested later in the season will be more bitter and astringent.

Another important factor affecting the bitter taste of tea is caffeine. Caffeine is the main alkaloid in tea, which generally accounts for 2%-5% of the dry weight of tea. Some studies have shown that the main flavor of caffeine is bitterness.
Bitterness of tea

Taste of tea

The oxidation products such as theaflvins and therubigins contribute to tea color and taste of the black tea. Moreover, tea quality is also determined by the processing techniques employed. The three basic types of tea; green, oolong and black have different quality characteristics, including aroma, taste and color, and appearance.

Compounds which contribute to characteristic tea taste are poly‐phenolic compounds, amino acids, caffeine, etc. Very complicated mixtures of volatile compounds, such as terpenoids, alcohols, carbonyl compounds, etc., contribute to characteristic tea aromas.

Taste of food is mainly composed of five basic sensations; that is, sweetness, astringency, sourness, bitterness and umami . A delicious cup of tea infusion is an ingenious balance of various taste sensations.
*Astringency is a drying, puckering sensation in the mouth that affects the whole of the tongue more or less uniformly. Tannin has a strong astringent or pungent taste. Tea has high tannin content. It congeals proteins on the top of the mucous membrane layer of one’s mouth and makes the tissues contract.
* Bitterness is usually unpleasant, but sometimes desirable in moderate amounts, and is perceived predominantly at the back of, and sometimes along side of, the tongue. Caffeine is the stimulant in green tea. Caffeine possesses a bitter taste, and the detection threshold is 3 ppm in water, which is 0.0003% .It, is important in tea flavor and briskness.
* The umami is a Japanese term, it is similar to the “meaty” taste or “brothy” taste.

Besides catechins and caffeine, some amino acids (such as arginine, alanine, etc) also contribute to the bitterness of green tea infusion. The amino acids in green tea area major factor in its quality, with about 20 different amino acids contributing to the overall content. Theanine accounts for more than 60% of the amino acids; theanine, glutamic acid, asparagines, arginine, and serine account for about 90% of total amino acids. Amino acids are mainly responsible for brothy taste. The umami taste of green tea infusion was shown to be due to some amino acids such as theanine, serine, etc and the sweetness to sugars.

Taste of tea