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

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.

Maturity Stages Almond Walnut

Tree Shaker almonds & walnuts

Windrow & Pickup almonds & walnuts

Concealed Damage of Almonds Storage at high temperature and relative humidity

Pick-up Machine for Walnuts

Walnut Hulling & Drying

Kernel Darkening from Sun Exposure

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

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

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.

Shake-Catch System for Pistachio Harvest

Sorting Pistachio Nuts to Remove Defects

Pistachio Hull Removal

Shell Staining

Shell Staining Scale for Pistachio Nuts

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

Pistachio Dryers Cross-Flow Continuous Belt

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)

Storage Potential

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

Water Activity of Selected Nuts and Dried Fruits & Vegetables

Equilibrium Moisture Content

Taste Placentia Perfection walnuts stored for 7 months at 72°F 9 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

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

Insects and Decay

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

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

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

Grain Aeration Components Perforated floor Metal grain bins Ventilation fan

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.

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

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.

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.