Tea chemistry 茶化學 2011

The chemistry of Tea

The chemical profile that determines the distinct tea character. The chemical composition of fresh tea leaves and processed green tea are very similar. Green tea contains the organic compound polyphenols, commonly known as catechins, which mostly include flavanols, but also contain flavandiols, flavonoids, and phenolic acids. The main process responsible for the chemical changes of tea is oxidation; oxidation is the process of polyphenol oxidase-dependent oxidative polymerization. Due to tea processing the chemical composition of black tea and fresh tea leaves are much different. Black tea contains bisflavanols, theaflavins, thearubigins, and other oligomers. The theaflavin is significant to the character of black tea. Theaflavins, which give the characteristic color and taste to black tea. Thearubigens, which are even more extensively oxidized and polymerized, have a wide range of molecular weights, and are less well characterized. Oolong tea, a partially oxidized tea, contains monomeric catechins, theaflavins, and thearubigins. Some characteristic components, such as epigallocatechin esters, theasinensins, dimeric catechins, and dimeric proanthocyanidins, are also found in oolong teas. With respect to dark tea and dark Puer tea, piling is the major process creating large chemical composition changes in the tea leaf. Changes in color, scent, and flavor all can be distinguished and identified. The microbe varieties, piling method, time period, weather, and type of fresh tea leaf all determine the character of the final product.

Common tea compounds affecting scent, flavor and color, as well as health benefits.

儿茶素 C catechin
沒食子兒茶素 EGC Epigallocatechin
沒食子兒茶素沒食子酸酯 EGCG Epigallocatechingallate
食子兒茶素 GC Gallocatechin
兒茶素沒食子酸酯 ECG Epicatechin gallate
兒茶素 EC Epicatechin
茶黄素 TFs Theaflavins
茶紅質 TRs Thearubigins
茶褐素 TBs Theabrownins
抗氧化剂 活性 AA Antioxidant Activity
挥发性香气组分 VFC Volatile fragrant compounds
叶绿素 Chlorophyll C32H30N4Mg
多酚類 PP Polyphenol
多酚氧化酶 PPO Polyphenol Oxidase
过氧化物酶 POD Peroxidase

Microbial fermentation and the piling process of Puer tea.

All Puer teas are made from large leaf Yunnan variety. Also to be called a Puer tea, it must first go through a series of determined steps which we have discussed in the processing section. Here let’s take a brief look at the piling process, elements, and microbes that determine the special character of dark Puer tea. By 1973 the Kunming Tea Factory had created the piling process of dark Puer tea. For the chemistry of piling to take place the tea leaves need water and with heat will give the suitable hot and humid condition, and the recently sun fixed leaves are piled, covered, left alone, and periodically turned and water is added when necessary, in order to catalyze the oxidation of non-enzymatic polyphenol compounds. This pile fermentation is done in the presence and action of certain microbes under controlled conditions. The key effect is to reduce the tea’s natural bitter characteristic and produce a full smooth flavor and texture. The piling process is due to certain colonies of microbes and it takes thirty to forty days for the desired chemical transformation changes. There are many parameters and requires extensive knowledge, skill, experience, and hygiene to be done safely and properly, piling involves some decomposition but it is controlled. Remember many types of microbes are a healthy part of our lives, examples, yogurt, wines, and cheese all have microbe growth, some can be seen like the tiny microbes grouped largely together can be seen in blue cheese. While the science of tea piling is still being researched and discovered below are some of the microbes involved in the piling process.

黑麯黴Aspergillus niger
青黴屬Penicllium
根黴司Rhizopus
灰綠麯黴Aspergillus gloucus
酵母屬Saccharomyces
土生麯黴Aspergillus terreus
白麯黴Aspergillus candidus

細菌類Bacterium


Comprehensive Introduction to Tea Studies (including Chinese-English Tea Terminology)
綜合研論茶學 (中英文茶之術語)
By: Steven R. Jones 作者: 瓊斯‧史迪芬 (2011.05, revised 2012.4)
第十三屆國際無我茶會 , 暨 國際茶文化節 , 論文集
Proceedings of the 13th International Wu-Wo Tea Ceremony and Tea Culture Festival
Pub.: 天仁茶藝文化基金會 Ten Ren Tea Arts and Culture Foundation
Date: 2011.05
ISBN: 978-986-84204-2-7
http://teaarts.blogspot.com/2011/06/comprehensive-introduction-to-tea.html