TEA, Pt. 2 - PROCESSING
Since all tea comes from the Camellia sinensis plant, the difference between the various types of tea comes down to processing. In tea processing, what we’re really concerned with is moisture content reduction. There’s no fruit to strip away as in coffee; we basically move right into the drying phase directly after harvest. Properly dried tea (down to about 3% moisture) can last for up to a year if stored properly - but fresh tea leaves hover around 70%. For every 1lb of tea produced, you’ll need about 4lbs of fresh leaves. Once tea is picked, processing is begun the same day in a processing facility known as a tea factory.
Through processing, tea can be transformed into white, green, oolong, black, or pu’er - primarily through the level of oxidization allowed. Chemically speaking, oxidization is the loss of electrons due to the interaction with oxygen. Oxidization can take many forms, including rust or the greening of copper. Oxidization in food is a familiar sight to anyone who’s ever left an avocado or a banana on their counter overnight. Oxidization begins when the cell walls inside the tea leaves are broken, through withering in the sun or being tossed. Various chemical reactions occur then - but most notably polyphenols are being converted into theaflavins and thearubigins. These are different polyphenolic molecules that are responsible for much of the flavor and coloring in the resultant beverage. The leaves will also turn brown as they dry. The rate and level of oxidization are unique to each tea produced. Tea factories will often change their methods from day to day, or even within the same day due not weather and atmospheric conditions. This is often considered the most skilled work in the tea making process.
There is an enormous amount of variance from tea to tea, but broadly speaking processing follows a few distinct steps. Fresh tea leaves are either lain out in the sun or placed on mesh racks with fans gently blowing warm air through to wither. This accelerates drying and helps to prevent mold growth. Leaves are then rolled in machines that look like two great disks to squeeze moisture out and further break down cell walls to encourage oxidization. Green and Oolong teas then go through a heating process to denature the enzymes that cause oxidization. This is known as “killing the green,” and can be accomplished several ways from oven baking to steaming. Black teas are left to fully oxidize. Some teas are then hand rolled for flavor or aesthetics, and others are charcoal roasted slowly to develop more flavors. In large part, oxidization level is what separates the different types of tea.