Postharvest Handling of Tree Nuts and Dried Products

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

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

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 drying to about 12% moisture – Ambient-air drying to 5 -6% moisture • Heated-air • Sun

Pistachio Dryers Cross-Flow Continuous Belt

Drying Temperature Drying Time Open shells – Temperature to 5 – 6% MC kernels released (°F) 140 160 180 200 (°C) 60 71 82 93 (h) 14 10 7 5 (%) 0 1 3 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 Hedonic Scale 9 Low quality Odor 8 Flavor 7 6 5 4 High quality 3 0 20 40 60 80 Storage Humidity (%) Placentia Perfection walnuts stored for 7 months at 72°F Rockland, 1957

Kernel Darkening Dark Kernels (%) 20 16 Serr 12 8 Pedro 4 0 0 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 °C Temperature °F 90 80 70 30 Red Bluff Sacramento 20 60 50 10 Maintain temperature as long as possible Cooling 40 30 S O N D J F M o n th M A M 0 J J A

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 k. Gy or higher

Experimental Insect Control Treatments –Fumigation with carbonyl sulfide, sulfuryl fluoride, or ethyl formate. –Controlled atmospheres (<0. 5% O 2 and/or 40 -60% CO 2). –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.