1. Postharvest Handling of Tree Nuts and Dried Products
Jim Thompson
UC Davis

2. Handle Chestnuts like Fresh Fruit Rather than Tree Nuts
Store at -1 to 0°C (30 to 32°F).
Cooling promptly to stop decay development and preserve quality.
Storage humidity = 90 – 95%.
Package in microperforated plastic film to minimize water loss.

3. Maturity Stages
Almond
Walnut

4. Tree Shaker almonds & walnuts

5. Windrow & Pickup almonds & walnuts

6. Concealed Damage of Almonds
Storage at high temperature and relative humidity

7. Pick-up Machine for Walnuts

8. Walnut Hulling & Drying

9. Kernel Darkening from Sun Exposure

10. Walnut Kernel Color Quality
Price is inversely related
to kernel color
Walnut Kernel Color Quality

11. Pistachio Maturity Pistachio shell split is desirable.
Early hull split is not desirable because it increases potential for fungal infection.
Pistachio Maturity

12. Pistachio Nut Maturity Indices
Ease of hull separation from shell.
Shell dehiscence (splitting).
Change in shell color (green to ivory).
Decrease in fruit removal force.
Kernel dry weight and fat content.

13. Shake-Catch System for Pistachio Harvest

14. Sorting Pistachio Nuts to Remove Defects

15. Pistachio Hull Removal

16. Shell Staining

17. Shell Staining Scale for Pistachio Nuts

18. Pistachio Drying Two-stage Heated-air Sun
Heated-air drying to about 12% moisture
Ambient-air drying to 5-6% moisture
Heated-air
Sun

19. Pistachio Dryers
Cross-Flow
Continuous Belt

20. Drying Temperature Should not exceed 71°C (160°F) Drying Temperature
Drying Time to 5 – 6% MC
Open shells – kernels released
(°F)
(°C)
(h)
(%)
140 60 14
160 71 10 1
180 82 7 3
200 93 5 6
Should not exceed 71°C (160°F)

21. Storage Potential

22. Storing Nuts & Dried Fruits and Vegetables
Water activity – maintain the dry chain
Temperature
Oxygen concentration
Effective insect control
Time
Cultivar

23. Water Activity of Selected Nuts and Dried Fruits & Vegetables

24. Equilibrium Moisture Content

25. Taste Placentia Perfection walnuts stored for 7 months at 72°F9
Low quality
Odor 8
Flavor 7
Hedonic Scale 6 5 4
High quality 3 20 40 60 80
Storage Humidity (%)
Placentia Perfection walnuts stored for 7 months at 72°F
Rockland, 1957

26. Kernel Darkening Dark Kernels (%) Storage Time (mo) 20 16 Serr 12 8
Pedro 4 3 6 9 12
Storage Time (mo)
Lopez et al., 1995

27. Insects and Decay

28. Insects cause Quality and Weight Loss
Navel orangeworm
Indian meal moth
Dried fruit beetles
Saw tooth grain beetle
Merchant grain beetle
Raisin moth
Fruit fly

29. Aeration to Control Storage Temperature and Humidity
Regularly ventilate storage with outside air to maintain uniform nut moisture in storage.

30. Average Air Temperature°F °C 30 20 10 3 4 5 6 7 8 9 R e d B l u f S a c r m e n t o
Temperature
Maintain temperature as long as possible
Cooling S O N D J F M A M o n t h

31. Grain Aeration Components
Perforated floor
Metal grain bins
Ventilation fan

32. Insect Control Procedures
Fumigation - methyl bromide, phosphine, propylene oxide.
Freezing at -18 ºC for more than 2 days.
Heat treatment (50-55 ºC).
Exposure to 100% carbon dioxide for more than 2 days.
Storage temperature <10 ºC reduces insect activity.
Storage in 0.5% oxygen (balance nitrogen) atmosphere reduces insect activity.
Irradiation at 750 Gy.

33. Sensory Quality of Irradiated Almonds
Quality is reduced at 1.5 kGy or higher

34. Experimental Insect Control Treatments
Fumigation with carbonyl sulfide, sulfuryl fluoride, or ethyl formate.
Controlled atmospheres (<0.5% O2 and/or 40-60% CO2).
Heat treatments (radiofrequency).
UV & IR radiation.

35. Reduce Losses of Dried Products
Dry below 0.65 water activity.
Store below 10°C (50°F), storage time increases with lower temperatures.
Clean storage before filling.
Protect from birds and rodents.
Insect disinfestation as needed.
Protect against reinfestation using insect-proof packaging.