Tea 102: Tea Processing

Below, we walk through each step, explain why it matters, and note how it varies by tea type.

Withering is the controlled removal of some moisture from freshly plucked leaves. It begins the moment a leaf is picked.

• Goals: soften the leaf so it handles and rolls without tearing, concentrate flavor precursors, and set up the chemistry for later steps.
• How producers measure it: by weight loss, feel, aroma, and leaf suppleness.
• Typical ranges: short to moderate withers for black and oolong teas, very short or even skipped for many green teas, longer and gentler for some white teas.

A note on caffeine: withering does not create more caffeine. As water evaporates, caffeine becomes more concentrated per gram of dry tea, but the total amount in the leaf does not increase.

Once the desired wither is reached, many teas move to rolling.

Rolling breaks some cell walls, mixing leaf juices with oxygen. This drives aroma development and sets the foundation for body and mouthfeel.

• Methods vary: traditional “orthodox” rolling uses pressure and motion to twist leaves, oolongs are often tossed or shaken to bruise edges, and CTC (crush-tear-curl) machines are used for some black teas to create small, strong-brewing pellets.
• Green tea: many green teas are first fixed to stop oxidation, then rolled primarily for shaping and texture. Others receive light shaping to limit cell damage.
• Other categories: oolong, black, and many dark teas, including pu-erh, are rolled during processing.

Cut an apple and it browns. Tea leaves behave the same way. When cells are exposed to air, enzymes catalyze oxidation that turns leaf compounds into new molecules, changing color and flavor.

• Chemistry in brief: catechins oxidize into theaflavins and thearubigins, which give darker teas their color and brisk or malty character. Chlorophyll degrades, revealing yellow to copper tones. Many other reactions shape the aroma spectrum.
• By type: green tea is not allowed to oxidize, oolong is partially oxidized on a spectrum from light to quite dark, black tea is fully oxidized.

Controlling temperature, humidity, and time during this phase is essential to achieve the desired profile.

Fixing, also called kill-green, uses heat to inactivate the enzymes that drive oxidation. Once fixed, leaves will no longer brown from enzymatic activity.

Common methods include:

• Pan firing, dry heat in woks or drums, classic for many Chinese green teas, often adding a toasty note.
• Steaming, the Japanese approach, which preserves bright green color and more vegetal or seaweed-like flavors.
• Heated tumblers or ovens, controlled hot-air systems used for many oolongs and some greens.

Clarifications:

• Sun drying is not a reliable way to stop oxidation, it is used for gentle drying or finishing in certain styles.
• Hot-water blanching is uncommon in tea manufacturing. Producers rely on dry heat or steam for consistent enzyme inactivation.

Shaping can occur before or after fixing, depending on the style. Leaves may be twisted, rolled into pearls, pressed flat like Dragon Well, or formed into cakes or bricks for dark teas. Shaping affects appearance, infusion rate, and sometimes flavor development during storage.

The final drying step reduces moisture to a safe level for storage, typically about 2 to 5 percent.

• Methods: hot-air conveyor dryers, oven or basket dryers, and fluidized bed dryers that suspend leaves on a cushion of hot air for even drying. Traditional sun drying is used for select styles, such as the maocha used to make raw pu-erh.
• Why it matters: drying too fast can trap grassy or harsh notes, drying too slow can lead to stale or musty flavors. Skilled producers balance temperature and time to protect aroma and color.

Some teas receive additional steps after drying:

• Roasting, low-and-slow baking that deepens sweetness and adds nutty or caramel notes, common in many oolongs and hojicha.
• Sorting and grading, to separate leaf sizes and remove stems or fibers.
• Aging or post-fermentation, microbial piling and maturation for dark teas such as ripe pu-erh, which creates earthy, smooth flavors.

• White tea: wither, gentle drying, minimal shaping, no fixing.
• Green tea: brief wither or none, fixing, rolling or shaping, drying.
• Oolong tea: wither, bruise and partial oxidation, fixing, rolling and shaping, drying, optional roasting.
• Black tea: wither, rolling, full oxidation, drying.
• Dark teas (including pu-erh): wither, often fixing and rolling for raw pu-erh, sun drying, then either pressed and aged (raw/sheng) or pile fermented before pressing and aging (ripe/shou).

Ready to taste how processing shapes flavor? Explore our curated samplers and compare a steamed Japanese green to a pan-fired Chinese green, or try a lightly roasted oolong next to a fully oxidized black tea. Our brewing guides and simple infusers make loose leaf easy.