According to a common rule of auction centers, a minimum batch of 300 kgs of
a particular grade of tea is necessary for a single sale. Most factories are not
equipped to produce that amount of a particular grade of tea in a single day's
operation. Thus it becomes necessary to store tea for a while in bins at the
factory as it is manufactured. And therein lies a problem. Tea, being a
hygroscopic body, tends to absorb moisture during storage for any length of
time. Various factors influence this moisture absorption.
Moisture Absorption Factors
Though auction centers stipulate a minimum of five chests of particular grade
of tea for a sale, buyers are found to favour batches of 30 chests or more.
Gathering a batch of that size would take most factories a number of days. In
any event, given conventional bins and usual weather conditions, this period
should not exceed two weeks so that excessive moisture absorption can be
avoided.
The capacity of the bin and the amount of tea it holds are important factors
in storage. If a bin is partly full, the moisture in the excess air would affect
the stored tea. In a filled bin, this affect is limited.
Construction and location of the bins
The construction and location of the bins are also important factors from the
point of storage. The bin should be designed with narrow cross section area so
that the tea will have low exposed surface, and it should be made airtight as
far as possible.
In addition, the bins should be raised off the ground and situated in a warm
dry part of the factory such as near the drying room where atmospheric air
maintains low humidity.
Being hygroscopic, tea releases or absorbs moisture according to atmospheric
conditions. It is found that the moisture content of tea has a linear relation
with storage conditions. Low moisture tea can be stored for a longer period that
high moisture tea. If stored airtight, low moisture will keep for a remarkable
long period without any loss of quality. The most suitable moisture range is 2
to 3% for storage in conventional bins for two to three weeks.
Weather Conditions during manufacture
The increase of moisture in stored tea is also influenced by weather
conditions. Normally, during the rainy season, tea can not be stored for more
than two weeks in conventional bins. But, if it the tea stored at 55-60%
relative humidity, corresponding to a hygrometric difference of about 10°F,
then the increase of moisture content would be limited, even conventional bins.
Each time a bin is opened, additional moisture is admitted into it. Hence,
where possible, the bins should be opened once tea is stored in them. This can
be done if the bin sizes and locations are designed with the output of the
particular factory's various grades in mind.
Source: Tea Technology, Gokul C. Sarma, P. Eng.
