Regeneration of Drying Beads

Efficient Drying and Safe Storage of
Agricultural Seeds and Products
Elizabeth Mitcham
University of California, Davis
Director, Horticulture CRSP
Director, Postharvest Technology Center
Seed Quality Is Essential for
Agricultural Productivity
Two key components of seed quality:
• Improved varieties
• High viability and germination capacity
– Produce high quality seed
– Store seeds with minimal loss of viability until
Zeolite Drying Beads
for the Seed Industry
Peetambar Dahal and Kent J. Bradford
University of California, Davis
Rhino Research, CABI, IDE, CEAPRED
Horticulture CRSP
Novel seed drying beads based on
zeolites (molecular sieves) make it
feasible to efficiently dry and
store seeds at low RH.
High Relative Humidity Shortens
Seed Storage Life
Seeds are very
sensitive to the
ambient relative
humidity (RH) of
the air.
Seed storage life is
reduced at high
relative humidity.
Humid Conditions in Tropical Regions Cause
Rapid Loss of Seed Viability
Ambient conditions in tropical regions often exceed 75% RH and
30°C during the monsoon season following seed harvest,
resulting in rapid seed deterioration in open storage.
Traditional Drying Methods Cannot Reduce Seed
Moisture Sufficiently under Humid Conditions
Seeds equilibrate with air
humidity. Air drying
cannot reduce seed
moisture content to safe
storage levels in humid
Alternative: Drying with Desiccants
Desiccants can be used to
absorb moisture from seeds.
Current desiccants have
drawbacks that have
prevented their widespread
use for seed drying and
Novel seed drying beads
based on zeolites (molecular
sieves) make it feasible to
efficiently dry and store seeds
at low RH.
Advantages of Desiccant Drying Beads
• Drying Beads can dry seeds to a specific and low MC
at ambient temperatures in moisture-proof
• Dry seeds inside moisture-proof containers are also
protected from molds, insects and rodents
• Seed quality is preserved for several years
• No need for cold storage to maintain seed viability
– Even for seed banks
Costs of Zeolite Desiccant Beads
• 0.3-0.5 beads to seeds ratio for one-step drying
• $10 to $20 per kilogram
– 100kg seed = 30 kg beads = $300 investment
• Less beads needed if initial drying by air first
• Dries to low moisture content within few days
• Beads can be regenerated by heating to high
temperatures up to 10,000 times
• Moisture-proof container needed
Regeneration of Drying Beads
Various ways to achieve high
temperatures needed for
regeneration of beads
• Electric oven
• Microwave
• Wood fire and other energy
• Simple device under
Service model could be
developed for regeneration of
beads for farmers microenterprise
Dry and Store Seeds using Beads
Other Storage Problems Are
Prevented at Low RH
Roberts EH (1972). Viability of Seeds. Chapman and Hall Ltd., Syracuse, NY, pp 14-58.
Pepper Seed Storage in Thailand
Before storage
After 6 mo storage
All seeds germinate
Higher seedling vigor
Open stored
Bead stored
Storage Insect Control using Drying Beads
Six months storage
Without beads
69% infestation
With beads
0% infestation
Courtesy of Keshavulu Kunusoth, ANGRAU, Hyderabad, India
Other Postharvest Applications
Drying of fresh horticultural products
Open-air drying:
reduction of 17% in 72 h
Drying beads:
reduction of 58% in 72 h
Chili peppers
Drying of Apple and Tomato Slices with Drying Beads
Ratio 1:8
Improved Solar Drying
2 meter stack to increase air flow
Build on earthen berm to maintain heat in evening
Air flow concentrated around drying product
Cheaper to build than standard cabinet dryer
Holds more product
Dried sliced tomatoes in less than half the time (2
• Finalist in international competition for drying
• Could be used for drying many products, including
grains and seed
Cabinet Dryer
Stack Dryer
Thank You!!

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