Fermented Tea or Oxidized Tea: What's the Difference?

Tea-culture is both science and art.  To produce a masterfully crafted tea requires both precision and intuition, the accuracy of the technique, and sheer inspiration, much like composing and performing music.

In both cases, science supports art. It’s valuable to use tea-terms carefully and to explain the tea-cultivating process and method as precisely as possible in order to more fully appreciate the next cup. An example is the word “fermentation”.

Teas are often described as semi-fermented, and fermented, and this is rarely the case. Teas are generally semi-oxidized and oxidized. The terms are often used interchangeably, but this may lead to confusion.

Freshly picked tea-leaves undergo enzymatic oxidation simply by exposing them to air and allowing them to dry. This process differs scientifically from how true fermentation is defined. “Ferment” generally requires the action of yeast, bacteria, or mold.

Part of the art of tea cultivating is deciding when to stop this oxidization process. This may be accomplished with steam, or dry heat, in various ways. Classically, this was done over wood-fire, charcoal, or heat vents.  Heating deactivates the enzymes which have been triggered by plucking the leaves, and determining when to step into the cycle is an example of tea-making mastery. This sense of timing is learned and taught, but also must be felt, in a less literal way.

If we are looking at the Camellia sinensis plant, a tea’s ultimate type will be determined by how much oxidization is allowed to take place. In their natural state, the leaves wilt if not dried soon after picking. As the chlorophyll in the leaves breaks down, the leaves darken, and tannins are released.

The mathematical possibilities begin to unfold as you contemplate the potential variations. White teas are traditionally wilted, and completely unoxidized. Green teas are both unwilted, and unoxidized. Oolongs are wilted, then bruised or “rattled” to an exacting level, and partially oxidized between 1%-99% depending on the artisans' result they are looking to reveal. Black teas are wilted, bruised, and fully oxidized. There are virtually unlimited nuances of variation possible between the plucking of the fresh leaf and the final blending, including adding florals, fruit, spice, and other elements before the mixture is steeped. Natural cycles, such as season and rainfall, also greatly affect the tea-leaf, its nature, quality, and character. All of these factors determine the lightness, depth, and flavor of the brewed tea.

The fact that the potential of the tea-leaf is unleashed merely by exposure to air—and not by the more chemically complex action of true fermentation—makes a cup of tea even more of a thing of wonder.

Want to learn more about tea? Check out our guide on all things tea here.

There’s an art to tea brewing too! Learn more here.