Some teas perk you up; others settle you down. That difference mainly comes down to three things in the leaf: caffeine (which drives alertness), L-theanine (which supports calm focus), and polyphenols (which shape bitterness/astringency and body). How much of each you taste and feel depends on the plant's cultivar, growing conditions, harvest season, plucking standard, and what happens after harvest (fixing, oxidation, roasting, fermentation, aging), as well as how you brew your tea leaves.
We'll break down what caffeine, theanine, and polyphenols actually are, how they act in the body, and how they interact with each other. We will explore how farming and processing influence these compounds and why brewing style matters. And by the end of this journey, you should have a better understanding of how to pick teas that lean "more lift" or "more calm", plus a few brewing adjustments to nudge the experience where you want it.
Caffeine in Tea
Caffeine isn't unique to tea. You'll also find it in coffee, cacao (chocolate), yerba mate, guaraná, and kola nut. Why do plants bother making it? – For defense. Caffeine is bitter and works as a natural repellent. That bitter taste helps discourage herbivores from chewing tender leaves.
Consumed, caffeine blocks certain receptors in the brain, reducing the "sleep pressure" feeling and sharpening alertness.
Tea's reputation for a steadier lift than coffee isn't because its caffeine is different (it's the same molecule), but because it's accompanied by another compound – L-theanine, and because we extract it differently when we brew. – We'll get to those interactions later. For now, let's see what affects caffeine levels in a tea leaf.
• The first factor is the leaf's age and plucking standard. Buds and first leaves generally carry more caffeine than older, larger leaves. Teas made with lots of buds or very young leaves (early spring Green tea, some Whites, certain Oolongs) often start higher for that reason.
• Next is the plant itself. All tea comes from the Camellia sinensis plant, which has quite a few botanical varieties, the most common of which are var. sinensis (small-leaf) – thrives in cooler, often higher-elevation regions across China, Taiwan, and Japan; and var. assamica (large-leaf) – prefers warmer, humid zones in Yunnan and much of South and Southeast Asia.
On average (but not always), var. assamica packs more caffeine than var. sinensis.
However, sinensis spans a broad range, depending on cultivar. For example, Japanese cultivars such as Yabukita, Saemidori, and Okumidori; Chinese cultivars such as Qi Dan and Fuding Da Bai; and Taiwanese cultivars such as Qing Xin and Ruan Zhi are all relatively high in caffeine. Cultivar alone doesn't fix a caffeine number, but combined with bud-heavy spring picking, it often nudges a tea toward a more energetic feel.
• Shading also affects chemistry. Covering bushes before harvest (as for Kabuse, Gyokuro, and Tencha for Matcha) raises amino acids and, as several studies show, also increases caffeine relative to comparable sun-grown leaves from the same fields.
• Caffeine is a fairly stable compound, and the usual tea processing, such as oxidation, kill-green, wither, roast, and microbial post-fermentation (such as in Shou Pu-erh and other Heicha), doesn't destroy caffeine. However, what changes is how readily it comes out. For example, in teas that are subjected to heavy rolling (Oolongs or Black (red) teas), the cell walls are compromised, allowing caffeine to be extracted more easily. Powdered Matcha is fully ingested, so you take in essentially all of it.
• Elevation also matters. High-mountain gardens grow cooler and slower, which makes plants concentrate more on producing amino acids rather than caffeine, since at high elevations, there is a lower threat from insects. A recent study found lower caffeine levels at higher altitudes than at nearby lowland sites (on the order of 20–25% reductions in the studied pairs). It probably won't hold for every tea garden and season, but it's a factor to keep in mind.
• Finally, brewing controls how much caffeine makes it into your cup, and how fast. In Gong Fu Cha, a high leaf-to-water ratio (about 1g:20ml) with very short steeps gives a noticeable lift in the first rounds but spreads total extraction over many small cups, so you can steer intensity step by step (cooler water or a shorter first infusion softens the start). In Western brewing (about 1g:100ml for a few minutes), most of the caffeine is extracted in a single prolonged infusion. A quick rinse won't "wash away" caffeine; most of it is stored well inside the leaf and comes out gradually, as you steep. Combined with cultivar and plucking choices, these simple brewing levers let you dial your session toward a brighter kick or a steadier, gentler curve.
L-theanine: calm focus in the cup
L-theanine is an amino acid that tea plants send into young leaves and buds. It's one reason a good tea session can give a feeling of clearness.
In the body, L-theanine interacts with glutamate pathways (the main excitatory system), nudging them toward a steadier state. Many people describe the effect as "calm alertness."
L-theanine increases alpha-wave activity – a marker of relaxed focus rather than sedation. Paired with caffeine, it smooths the edges.
What determines how much theanine the leaf starts with?
• First, leaf age and season. Once again, early spring, bud-heavy plucks are usually richer in free amino acids, including theanine. As the season warms and leaves mature, free amino acids in the leaf usually decrease, while catechins and other phenolic compounds increase as part of the plant’s defense, so second- and third-flush teas tend to taste less savory and feel a bit sharper. Sun vs. shade is the big lever growers use: shading (Kabusecha, Gyokuro, Tencha) slows photosynthesis and preserves theanine, which is why shaded Japanese teas taste sweet-savory (umami) and can feel both energizing and composed. In full sun, theanine is used up more quickly, and catechins rise.
• Variety and cultivar also matter. The small-leaf var. sinensis has many named cultivars selected for a pleasing amino-acid balance. In Japan, Saemidori, Okumidori, Samidori, and Asahi are standouts for high amino acids under shade (great for Gyokuro and Matcha). In China and Taiwan, cultivars like Qing Xin and Ruan Zhi, when picked early and not subjected to heavy processing, show a sign of good amino-acid content even outside of shading.
On the large-leaf var. assamica side, free amino acids at harvest are often lower due to sun-grown, mature-leaf picks – not because assamica "can't" make theanine, but because the plucking standard and growing conditions push chemistry toward sturdier, more phenolic leaves.
• Growing elevation matters, but not in a straight way. High-elevation gardens get more cloud cover and diffuse light. That mimics gentle shading: leaves grow more slowly, stay tender, and tend to keep more free amino acids and soluble sugars while building fewer astringent and bitter catechins than sun-blasted lowland leaves. Even though studies don't always show a clean "altitude leads to more theanine" evidence, the package of cool temps + softer sunlight + slower growth consistently points the cup toward umami and sweetness.
• Processing changes the amino acid levels. Kill-green locks in the fresh profile, including theanine. High-mountain Oolongs are usually lightly oxidized and lightly roasted. That preserves free amino acids and aroma glycosides. With extended oxidation (as in Black teas) and heavier roasting (as in Wuyi Oolongs), free amino acids gradually decline as they participate in browning and aroma-forming reactions; the cup tastes rounder and less overtly savory. Post-fermented teas (Shou Pu-erh and other Heicha) bring microbes into the mix. During piling, microbes and heat drive reactions that reduce L-theanine. The mellow feel of the liquor comes mainly from changes in polyphenols rather than extra theanine. Aging also reduces the amount of amino acids over time.
• Brewing determines how much theanine you actually consume and how it feels alongside caffeine and polyphenols. Theanine is very water-soluble and extracts well at moderate temperatures, so cooler water emphasizes sweetness/umami without dragging out a lot of bite. That's the logic behind low-temperature Gyokuro sessions. In Gong Fu Cha, short infusions let you keep the first cups plush and savory by easing the temperature and time; you can lengthen later steeps and up the water temperature as the leaves open. In Western brewing, controlling temperature is your primary tool – drop it for Green and lightly oxidized teas if you want a sweeter, calmer cup. With Matcha, you ingest the ground leaf, so all the amino acids are in play alongside the caffeine from the start; dose and water temperature are your levers.
How does theanine make us feel? Think of it as a counterweight: it doesn't cancel caffeine, but it often tempers jitter and supports a steadier, clearer mood.
That's why shaded teas like Gyokuro and Matcha can feel both energizing and composed, and why a fresh high-mountain oolong can deliver better focus. If you want more of that calm-focus profile, look for early spring picks, shade-grown material, and keep your water temperature not too high. If you prefer a stronger kick, use hotter water or choose sun-grown, later-season lots, where theanine naturally plays a smaller role.
Polyphenols in Tea
Polyphenols are a big family of plant compounds that shape tea's taste, color, and body. In green and lightly processed teas, the main players are catechins (EGCG, EGC, ECG, EC). When leaves are oxidized (as in Oolongs and Black teas), catechins link up to form theaflavins (bright, brisk) and then larger thearubigins (body, color). In post-fermented teas (Shou Pu-erh and other Heicha), microbial action and slow oxidation push things further toward heavier theabrownins. Polyphenols are responsible for bitterness, astringency, color, and body, which is why a tea can feel sharper or more rounded even when caffeine hasn't changed.
• What raises or lowers polyphenols in the leaf? Let's start with leaf age and plucking.
Young leaves contain plenty of catechins, which taste bitter and have a drying effect.
So, bud-heavy spring greens can be vivid and brisk. As leaves mature, total catechins often rise with sun exposure, but the cup can read softer because larger leaves bring more cellulose and fewer tip aromatics; it depends on how they're processed.
• Sun vs. shade is a clearer lever: catechins serve as protectants against UV light, similar to the sunscreens we use when we go outdoors. So, full sun increases catechins, while shading preserves amino acids and suppresses catechin buildup, yielding sweeter, umami-forward cups.
• Variety/cultivar sets the baseline chemistry. Small-leaf var. sinensis includes many cultivars selected for balance; large-leaf var. assamica, grown in warmer climates with lots of sunlight, often shows higher catechin content.
• Elevation also plays a role. Cool, cloudy high-mountain conditions slow growth and soften direct light (due to fog, clouds, and mist), often resulting in lower catechin accumulation relative to comparable lowland, full-sun leaves. That's part of why high-mountain oolongs taste clean and creamy: cooler temps, diffused light, and tender material.
• Processing plays a big role in the transformation of polyphenols. Kill-green halts oxidation and preserves catechins (Green teas & lightly oxidized Oolongs). With partial oxidation (deeper-oxidized Oolongs), some catechins convert to theaflavins, adding golden color and a lively, tea-tannic snap. Complete oxidation (Black tea) builds more thearubigins, deepening color and body while softening the initial bitterness. Heat from roasting drives Maillard-type reactions between sugars and amino acids and can round harsh edges, even when the total polyphenol content per gram doesn't drop much. In post-fermented teas, microbes reduce catechins over time and increase theabrownins and free gallic acid, which is why Heicha feels mellow, earthy, and less astringent. Aging continues polymerization and slow oxidation, so aged Raw Pu-erh loses bite and gains depth.
• Extraction is where you feel all this in the cup. Polyphenols are water-soluble, and hotter water + longer steeping time = more bitterness and astringency. Leaf size and condition matter: broken leaves release polyphenols fast. Brewing style sets the curve. In Gong Fu Cha, a high leaf-to-water ratio with very short steeps lets you manage the polyphenol surge – early pours can be sweet and plush if you keep the water moderate, then you can lengthen later steeps and raise the water temp as the leaves open. In Western brewing (about 1g:100ml for a few minutes), you extract a significant share in one pass; if a tea gets edgy, cool the water or cut the steeping time to keep astringency in check.
Higher catechins tilt a tea toward brisk, "awake" perception even though they aren't stimulants. Oxidation and roasting soften roughness, so the same caffeine can feel calmer in a well-oxidized oolong or an aged tea than in a punchy spring green. And because shaded teas hold more amino acids and fewer catechins, they taste sweeter, especially at lower temperatures.
Takeaway.
Caffeine sets the "wake-up," L-theanine steadies it, and polyphenols decide whether the cup feels sharp or smooth.
If you want steady energy, look for teas with both caffeine and theanine: shaded Japanese Greens (Gyokuro, Matcha; cultivars like Saemidori, Okumidori, Asahi) and early-spring, tender-leaf Oolongs (Qingxin, Ruan Zhi). For a brighter kick, choose sun-grown, bud-heavy spring Greens, lightly oxidized Oolongs from lower elevations, Dan Cong Oolongs, or Raw Pu-erh. For a calmer session, reach for later-season, larger-leaf Oolongs, well-oxidized/roasted Oolongs (Tieguanyin cultivar, Wuyi Oolongs), many Hongcha, or post-fermented Heicha; they're typically more rounded and feel smoother even when caffeine is present.
Buying cues: check labels and notes for cultivar, shading, harvest season, and bud content. Oxidation/roast hints: heavier oxidation/roast = rounder, less edgy taste and mouthfeel; lighter oxidation = brisker flavor. Pick shaded Japanese teas for calm focus; pick sun-grown first flush for energy spike; pick aged/roasted/post-fermented tea to unwind.
Brewing cues: control temperature, time, and ratio. Gong Fu Cha (~1g:20ml, short steeps) lets you ramp intensity gradually – cooler water or shorter first pours = gentler curve. Western (~1g:100ml, a few minutes) extracts a large share at once. – Drop the temperature or steeping time if the cup edges up. Powdered tea (Matcha) delivers everything immediately as we consume the whole leaf, in powdered form, mixed with water. – Manage dose and water temp.
With these levers and a quick read of cultivar, shading, season, and processing, you can reliably nudge your tea session toward more lift or more calm.