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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.
- 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.
Pistachio Drying
• Two-stage– Heated-air drying to about 12% moisture
– Ambient-air drying to 5-6% moisture
• Heated-air
• Sun
Drying Temperature
Drying Time to 5 – 6% MC
Open shells – kernels released
(°F) (°C) (h) (%)
140 60 14 0
160 71 10 1
180 82 7 3
200 93 5 6
Drying Temperature
Should not exceed 71°C (160°F)
Storing Nuts & Dried Fruits and Vegetables
• Water activity – maintain the dry chain
• Temperature
• Oxygen concentration
• Effective insect control
• Time
• Cultivar
Rockland, 1957
Placentia Perfection walnuts stored for 7 months at 72°F
3
4
5
6
7
8
9
0 20 40 60 80
Storage Humidity (%)
Hed
on
ic S
caleOdor
Flavor
Taste
Low quality
High quality
Kernel Darkening
0
4
8
12
16
20
0 3 6 9 12
Storage Time (mo)
Dark
Kern
els
(%
)
Pedro
Serr
Lopez et al., 1995
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
Month
30
40
50
60
70
80
90
S O N D J F M A M J J A
Sacramento
Red Bluff
Cooling
Tem
pera
ture
30
20
10
0
°F °C
Maintain temperature as long as possible
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.
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.