The production of raw (sheng) pu erh tea involves a deliberate balance in processing to allow for ongoing natural aging, which relies on residual enzyme activity and microbial fermentation. Let’s break this down step by step, addressing your points about partial sha qing (the “kill green” or fixation step) and the steaming during cake compression.

Sha Qing: Partial Deactivation of Enzymes After the tea leaves are picked and withered, they undergo sha qing, typically by hand-roasting them in a large iron wok over firewood (traditional method) or sometimes via machine. This step heats the leaves to deactivate most of the oxidative enzymes (like polyphenol oxidase) that would otherwise cause rapid browning and decomposition, similar to how green tea is processed to “lock in” its fresh character.

However, for raw pu erh, sha qing is intentionally milder—done at lower temperatures or for shorter durations compared to green tea. This leaves a small portion of enzymes active, along with some moisture in the leaves. The goal isn’t full deactivation (which would make it taste like green tea and prevent aging) but rather to slow oxidation enough to stabilize the leaves while preserving potential for gradual transformation. After sha qing, the leaves are rolled to bruise them slightly (promoting minimal oxidation) and then sun-dried, which further retains trace enzymes and sets the stage for long-term aging through slow enzymatic activity and microbial involvement.

Without this partial approach, the tea would spoil quickly or fail to develop the complex, mellow flavors that raw pu erh gains over years (or decades) of storage.

Steaming During Cake Production: Not a Full Denaturation Once the loose tea (called maocha at this stage) is ready, it’s often compressed into cakes, bricks, or other shapes for storage and aging. To do this, the dry maocha is briefly steamed—typically for just 20-30 seconds over hot steam jets—to soften and moisten the leaves, making them pliable and sticky enough to hold together under pressure (either manual stone pressing or hydraulic machines). The steamed tea is then wrapped in cloth, pressed, and allowed to dry slowly on racks.

This steaming is not equivalent to autoclaving or a prolonged heat treatment that would fully denature all proteins/enzymes. Key reasons why it doesn’t “kill everything”:

Brief Duration and Purpose: It’s a short, targeted exposure (seconds, not minutes) aimed at physical softening, not enzymatic destruction. The leaves are already dried at this point, so they have lower moisture content than fresh leaves, which limits how deeply the heat penetrates to affect enzymes. Comparison to Sha Qing: Sha qing is the primary enzyme-deactivating step earlier in processing. The later steaming is milder and doesn’t replicate the intense wok heat that partially “kills” enzymes—it’s more like a quick rehydration. Aging Continues Post-Compression: Raw pu erh cakes are designed to age naturally after pressing, developing deeper flavors through residual enzymatic oxidation (from the surviving leaf enzymes) and, more importantly, microbial fermentation (bacteria, yeasts, and fungi that colonize the tea). If steaming denatured everything, this aging wouldn’t occur—but it does, as evidenced by how young raw pu erh starts astringent and floral, then evolves to smoother, earthier notes over time. Not Like Ripe Pu Erh: For contrast, ripe (shou) pu erh involves a separate wet-piling fermentation step before compression, where enzymes are more fully deactivated to mimic accelerated aging. Raw pu erh skips this, preserving activity for natural progression. In essence, the steaming doesn’t undo the careful partial sha qing—it’s a mechanical aid that keeps the biological elements intact for the tea’s signature slow evolution. If you’re sourcing raw pu erh, look for well-stored cakes from reputable Yunnan producers to experience this aging firsthand