Green Tea Chemistry 101: Key Compounds for Flavor Quality

Pleated leaf face typical of var. assamica

If you are a lover of tea, you’ve likely had a cup of tea that made you go “wow.” That moment of tea-induced bliss is where the life-long passion for tea often begins.

But why in particular was that cup of tea so especially delicious? What contents of that brew made it so enjoyable to drink? Why do some cups make you say “wow” and others make you say “meh.” Let’s try to understand this “wow” factor by breaking down the constructs of green tea flavor, particularly what makes great green tea flavor great.

First and foremost is tea polyphenols (TP). Most polyphenols in tea belong to a category called catechins, also known as tannins, representing about one-third of solids in a cup green tea. Tannins exist in many other foods and beverages, such as red wine. They function in most plants as a type of sunscreen, in that they are able to take UV radiation from the sun and dissipate it so it does not damage cells. 

Tannins are bitter/astringent in nature, playing a big role in determining the perceived “strength” of the body of green tea taste. Tannins need to be abundant enough in the tea infusion so that flavor is not too weak, or thin. At the same time, too many tannins will make the infusion unpleasantly bitter/astringent. Probably most of us have had tea in the past that was too tannic. 

Overly tannic tea infusions result from tea tree growing conditions, or over-steeped tea. Summer months generally cause the highest tannin content in tea leaves, since this is when the leaves need the UV-fighting power of tannins the most. Also, higher water temperatures, and longer steep times pull more tannins out of the leaves. 

So, a big reason why that green tea infusion made you say “wow” is that your leaves were steeped enough, but not too much, keeping tannin levels in check. Experts tend to agree that tannin content in green tea is best right around 20%-24%. 

The following green tea compound separates “good,” from “I am weeping this is so so tasty.” Amino acids. 

Amino acids stand for only 1%-4% of solid compounds in tea leaves, but account for most of the savory and sweet flavor in green tea. The pleasant flavor of amino acids is what helps to mask the bitterness/astringency brought by tannins. There have been 26 different amino acids discovered in tea leaves so far, L-theanine being the most prevalent among those (accounting for 50%-70% of all amino acids in a tea leaf). 

Amino acids are essential to plant health, as they function as building blocks for other compounds, such as proteins, tannins, and aroma compounds. This means that savory amino acids can actually be transformed into bitter tannins under certain growing conditions (conditions of strong sunshine). For that reason, a primary objective in green tea production is minimizing the conversion of amino acids into bitter tannic compounds. 

So, we can most likely assume that when you drank that memorable cup of green tea, smacked your lips together in satisfaction, and said “YUM!”, it was at least partly due to a tea infusion rich in amino acids.

Tea heading into the oven to dry

You might be thinking, “if tannins should be kept on the low end, and amino acids on the high end, then there must be an ideal ‘tannin to amino acid ratio,’ a quantified value, that we are seeking to find.” To this I would say, “you are bizarrely perceptive, and exactly right!” The tannin/amino acid ratio is a figure that is commonly calculated when running quality control testing on batches of green tea. Ideally, this tannin/amino ratio should be kept relatively low. 

It is worth emphasizing that this is a ratio, meaning that a great green tea can still have a high amount of tannins, so long as there is also a high amount of amino acids to balance things out. 

Your “wow” flavor likely came from a tannin content between 20% and 24%, accompanied by however many amino acids that little tea tree could pump out, ultimately dropping the tannin/amino ratio as low as possible. 

What else creates that mouth-watering flavor in our teacup? … Sugar! 

Soluble sugars team up with select amino acids to offer sweetness to the tea infusion. While sweet is not the typical flavor attributed to green tea, tea leaves do contain a measurable portion of carbohydrates (20%-25% of solids). These carbohydrates include cellulose, starch, glucose, etc., which can be broken down during processing into soluble sugars that add a touch of sweetness to your tea. 

Soluble sugars, along with sweet and savory amino acids, serve to counteract the bitterness/astringency of tannins in green tea, while still allowing tannins to provide structure to the infusion. The result of synergy among tannins, aminos, and sugars creates a flavor profile that is strong, brisk, and refreshing. 

In addition to adding sweetness, soluble sugars and amino acids are viscous, enhancing the roundness and thickness of mouthfeel. The sweet, savory, and viscous attributes of sugars and amino acids balance out the bitter and astringent tannins to orchestrate polyphenol perfection, bringing about a sip followed by a “yum.” 

Gongfu Cha (工夫茶)

What about you, the infuser and composer of this flavor symphony? What is your role in orchestrating the tastiest infusion possible?

Rule number 1, do not use fully boiled water. Do not even boil the water then let it cool down. Once the water has been brought to a roaring boil, CO2 has been evaporated out, pH goes up, and extraction yield goes down. bad for flavor

Additionally, high infusion temperatures extract more tannins and less amino acids, while the opposite is true for lower infusion temperatures. But, cold-brewing takes longer, and I want my tea now. So, we can compromise by infusing green tea around 80 degrees C (175 degrees F). This temperature ensures you are extracting enough material here and now, while not disrupting our precious tannin/amino acid ratio. 

Another tip: refrigerate your green tea. Some teas can be stored in a closet for ten years and emerge with even better flavor… green tea is not one of those teas. Green tea should be kept fresh, and be consumed within the same year it was produced and purchased. 

Tannins are higher in green tea than in other teas, and those tannins deteriorate relatively quickly. While tannins should be kept below a limit, they also should be kept above a limit, letting the tea maintain a crisp taste and a full body. Refrigeration slows the deterioration of tannins, just like refrigeration slows deterioration of fruits and vegetables. 

Frosty tips of an organic field in Guizhou

However! When refrigerating your green tea, do not put it inside your cheese drawer, or next to the minced garlic, or pickled cabbage. Tea leaves take on foreign scents quite easily, which is convenient for producing scented teas, but inconvenient for storage efforts. Unless you want cheesy pickled cabbage tea, try your best to use smell-proof packaging, and give your tea it’s own little space in the fridge (it deserves it). 

WELP, that’s a brief tidbit on understanding the ‘wow-factor’ in green tea. If you have two green teas, try an experiment by brewing them identically and see which has a relatively sweet and savory flavor profile, possessing not too much bite, but still just enough body. Is the mouthfeel flat? Overly astringent? Is there roundness/thickness to it? 

Think about ratios, balance, and the ideal tannin/amino middle ground. Most of all, when you find that green tea that you absolutely love, yell “YUM” at the top of your lungs!! Or just smile inwardly. 

Thank you for reading. Please feel free to reach out with questions/comments/feedback, etc., and check out @WuMountainTea on IG for pics with informative captions. 

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