What does “drying” mean in tea processing?
An important step of tea processing, and something that all teas must go through to be considered shelf-stable is drying. Drying both makes the tea leaves shelf stable and enhances their flavor. At times, these can be two distinct steps in processing; at other times, it can be seen as more of a continuum. Sometimes teas are only dried for shelf-stability. For our discussion here, I’ll explain each separately.
Most Common Drying Methods
- Commercial dryers: perforated conveyors move the tea leaves through a heat source in an endless chain. Leaves can also be moved through fluidized bed dryers and dried on a bed of hot air (see an endless chain dryer in the photo above).
- Oven drying: tea leaves are set on perforated trays in an oven and hot air is circulated through the tea via convection.
- Sun drying: tea leaves are spread outdoors (usually on shallow bamboo baskets) to dry in the sun.
Less Common Drying Methods
- Charcoal firing: tea leaves set in a shallow bamboo basket are heated slowly over hot coals.
- Drying on heated floor: where tea leaves are dried on a thick masonry floor heated from below.
Drying for Shelf Stability
Drying for stability means reducing the moisture level in the tea leaves to 2–3%. Doing so makes the leaves shelf-stable and slows the oxidative processes within the leaves to nearly a full stop. Tea makers control the temperature of the air, the volume of air moving past the tea, and the amount of time that drying occurs to produce a palatable tea. Drying the tea too slowly results in stewing, and drying it too quickly results in the outside of the leaves drying much quicker than the inside, a condition known in tea production as case hardening. According to India’s Tocklai Tea Research Institute, “an average loss of more than 4% moisture per minute leads to bitterness and harshness in made tea. Moisture loss at 2.8–3.6% per minute has been found to produce teas with good quality.”
Drying for Flavor Enhancement
Drying for flavor enhancement refers to two optional processing methods known as finish-firing and roasting. Both involve heat, and both can be seen as distinct processing steps or part of drying for shelf-stability. Not all teas are finish-fired or roasted; typically these processes are reserved for higher-end teas and are skipped in commercial tea production. This type of drying alters the taste via the pyrolysis of the amino acids and sugars in the tea leaves.
Finish-firing refers to a very low temperature heating of tea leaves for several hours, typically in an oven or in shallow bamboo baskets over hot coals. After the leaves cool, they are immediately packed and shipped. This enhances the flavor and aroma of the leaves but doesn’t necessarily change it.
Roasting, on the other hand refers to a method of heating that is meant to change the flavor and aroma of the tea, typically adding toasty, burnt notes and resulting in a darker tea and a darker infusion depending upon how long the tea is roasted and at what temperature. Roasting also occurs in an oven or in shallow bamboo baskets over hot coals.
Featured image credit: Michael Petersen of Tealet.