Drying, cleaning and upgrading
Drying-
In order to facilitate processing, to prevent losses in germination and to reduce the
chances of insect attacks during storage, seeds must be dried to an appropriate level.
Drying generally involves the removal of moisture distributed inside the whole seed.
Advantages of seed drying
- Permits easy harvest
- Permits long-term storage
- Permits more efficient use of land
and man power
- Permits seedsmen to sell a better
quality product
Methods
of drying:
Sun
drying / natural drying: Natural drying is done by spreading the seeds on trays, floors or
fields on the open sun. The main advantage of this method is that it requires no
additional expenditure. The disadvantages are delayed harvests, risks of weather damage
and mechanical mixtures.
Artificial
drying: Involves passing of heated or unheated air through the seeds to remove moisture.
In unheated drying air should have low relative humidity hence it is not effective in
moist weather. Heated drying is quicker, faster and requires less drying space but the
disadvantages are high initial costs, damage of fire and possibility of overheating the
seed.
Cleaning
and grading:
Cleaning:
The
seed from threshing floor is mixed with seeds of other crops and of weed seeds, pieces of
straw, gravel, soil etc. In the cleaning process the separation of undesirable material
from desirable material is done on the basis of differences in physical properties. The
principle differences found in seeds are seed size, density, shape, surface texture,
colour, etc.
Methods of cleaning seeds:
- Preparing seeds for basic seed
cleaning (Pre-conditioning and pre-cleaning of operations)
- Basic seed cleaning operation
- Upgrading the quality of cleaned
seed
Different machines are available to
separate seeds from inert matter. For e.g. specific gravity separator divides seed on the
basis of weight and size, pneumatic separator separates seeds on the basis of there
resistant to overflow, spiral separator separates them on the basis of seeds shape.etc
Grading: is the removal of smaller
and shrivelled seeds from the well field healthy seeds. In India, air and screen machine
is extensively used for cleaning and grading purpose. |
