Sunday, August 4, 2013

Withering Readies the Tea Leaf for an Assault

Freshly withered leaves.
The first step after harvesting leaves from the tea plant, Camellia Sinensis, is to wither the leaves.  Withering is the reduction of moisture and the softening of the freshly picked leaf.  The point of withering is to prepare the tea leaf for the assault of processing.  For green, oolong, yellow and black teas, the tea leaves will be crushed, pummeled, rolled and pressed via hand or machine.  Why the assault?  To force the juices from the inner structure of the leaf to the surface to get oxidation going.  Oxidation is the chemical change that occurs when enzymes in the juices react with oxygen in the air of the surrounding environment.  The final tea product is defined in part by the amount of oxidation achieved in processing.  White tea is generally not oxidized; green tea gets the least amount of oxidation; and oolong and black tea get quite a bit of oxidation – which equates to more assault for oolong and black tea leaves. 

Leaves after assault of processing.
OK, let’s get technical.  There is a physical and chemical aspect to withering which conditions the leaf for the assault stage of processing.  In the physical aspect of withering, moisture content is reduced which makes the leaf become soft, slightly rubbery and flaccid enough to withstand assault without breaking.  A “soft” wither retains a higher percentage of moisture in the leaf, whereas a “hard” wither retains less.  In the chemical aspect of withering, large organic compounds break down into more simple molecules, a natural process that begins the moment the leaf is plucked.  Proteins degrade to amino acids which initiate aroma compounds.  Volatile Flavor Compounds (VFC) develop and increase in intensity the longer the wither. “Liquors from fresh leaf are bitter, but in well-withered leaf, sweetness develops.”[1]

Freshly harvested leaves laid out to wither.
Photo credit: Chris Falter
Withering time can be expected to range from 12 to 16 hours [2], but that can vary greatly due to humidity and temperature of the region.  Typically the leaves are laid out evenly to wither at their own natural pace, but sometimes they are helped along by warm air blown over them, or heated pans under them.

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