You see a friend at the cafe with a cup of golden sunshine. Ah, Shelly’s a tea drinker, you think. That’s about right, she’s so smart and relaxed and witty. So you sonder over to your tea-loving friend and inquire, “Hey, Shelly, what’s in the cup?” Shelly, with a sly grin, replies, “It’s chemistry.” “Chemistry?” you ask, with puzzled amusement, “I thought that was an oolong.” She draws closer as not to disturb the mocha sippers and the cafe au lait drinkers nearby. “Yeah,” she says, “it’s veritably steeped in it.” You both have a good chuckle because word play suits you and you’re smitten by her sophisticated humor.

Okay, that either elicited a slight smile or I’ve already lost you, which means the remaining text may not totally be what you’re looking for. And that’s okay! Each post here isn’t for everyone all the time. But if you stay with me we’re going to have a look into a topic that I find fascinating – the chemistry of tea. It’s my hope that by sharing this information we can better understand what’s happening in our cup, how that impacts the flavor of tea and how to make informed decisions about what you’re drinking next.

There are hundreds of chemicals present in tea, but we’re primarily focusing on a few groups of compounds that have the greatest impact on flavor, aroma and appearance in the cup. What’s really remarkable is, while I’m referencing research that was undertaken in the last decade or so, growers and tea drinkers have understood these concepts for thousands of years! (At the bottom I’ll reference a few terrific sources for further reading.)

Polyphenols

When people talk about the amazing health benefits of tea, they’re mostly noting polyphenols. These compounds include flavonoids, which are powerful antioxidants and are found in great supply in young tea leaves and buds that were grown with plenty of sunlight. This is because the sun converts amino acids into polyphenols. Chinese green tea is a prime example of sun-grown young tea that is loaded with polyphenols. The presence of these compounds also give tea its characteristic astringency. Fun fact: polyphenols are also a natural part of the plants’ defense mechanism against pests. 

Amino Acids

So if sunlight converts amino acids into polyphenols, what happens when tea is grown in the shade? You get the classic profile of Japanese green tea. When amino acids are in greater supply, they impart sweetness and brothiness to the tea. This is the umami flavor that’s prized particularly in Japanese teas, which are mostly shade-grown for this effect.

Amino acids include the compound L-Theanine, which can supply up to 60% of the amino acids in tea. L-Theanine is the focus of researchers because it produces alpha brain-wave activity, which promotes relaxation. In fact, L-Theanine works collaboratively with caffeine in tea to help us stay alert while supplying a sense of ease, something Buddhist monks have known for thousands of years as they’ve used tea to support meditation!

Enzymes

Enzymes play a role in the browning of tea leaves during their processing. In the oxidation step of tea-making, this “enzymatic browning” transforms the characteristic greenness of a green tea into the characteristic blackness of a black tea, and can be halted at anytime by either supplying sufficient heat (approximately 150F) or reducing the moisture content to denature the enzymes. This is the exact same reaction that occurs in other fruits and veggies that turn brown over time.

Pigments

Pigments are triggered by enzymes and also influence a tea’s color. Notably, the pigments found in tea includes carotenoids. These are compounds that degrade during processing to form demascenone, which is intensely sweet. Since mature leaves contain higher concentrations of carotenoids, and since oolongs are generally made from older, more mature leaves, it’s the presence of demascenone that gives this tea style its characteristic sweetness!

Carbohydrates

Tea is virtually a calorie-free beverage, though carbohydrates in the form of sugars and starches are chemically present. Carbohydrates help fuel the creation of polyphenols in young tea leaves and also contribute to the sweetness of tea’s flavor. 

Methylxanthines

The methylxanthine most discussed in tea is caffeine, but others, including theobromine and theophylline, are present and help ward off insects in growing leaves. Because of their alkaline properties, these compounds contribute a slight bitter flavor.

A quick note on caffeine: while similar to the caffeine found in coffee, which stimulates the central nervous system and the cardiovascular system, the caffeine in tea does not stimulate the coronary system (i.e., increase blood flow). This means that the “jitters” that can accompany coffee consumption do not have the same result from tea. Also, notably, catechins (a polyphenol) bond to caffeine molecules when we drink tea. Over time this bond is weakened and the caffeine is then absorbed into our body, meaning tea’s caffeine can have a time-released quality.

Minerals

Minerals are important body regulators and are present in brewed tea. There are 28 identified minerals in tea, with a relative high amount of fluorine, manganese, arsenic, nickel, selenium, iodine, aluminum and potassium.

Volatile Aromatics

When tea is brewed, these volatile aromatics escape as vapor into the air and reach our olfactory system (tiny nasal membranes that respond to aroma). While volatile aromatics comprise 0.01% of the dry weight of tea leaves, they contribute significantly to the sensory appeal of tea through smell. In tea there are hundreds (and possibly thousands!) of aromatic compounds, leading to a complex and fascinating bouquet that changes from tea to tea.

If you made it this far in the article, congratulations! You’re a certifiable tea nerd and science junkie – welcome to the club. There’s always more information to explore, so what follows are links to more information about the science of tea. Have fun, nerds!

Tea: A User’s Guide – Tony Gebely
Tea Chemistry – Matthew Harbowy and Douglas Balentine
ChemistryWorld.com “Uncovering the the Secrets of Tea” 
Food Science and the Culinary Arts – Mark Gibson 
Tocklai Tea Research Association