Nuts & Fruits, Dried

MATURITY & QUALITY

Maturity Indices 

Nuts. Hull splitting, hull separation from the shell, shell splitting, decrease in fruit removal force, drying of hull and kernel.

Dried Fruits. Fruits destined for dehydration must be harvested firm-ripe to obtain good-flavored dried fruits.

Quality Indices

Nuts. Color; texture (crispness); flavor: development of staleness and rancidity; moisture content; incidence of decay-causing fungi; insect damage. Nuts in the shell have longer storage potential than shelled nuts. Broken pieces are more perishable than halves or whole kernels.

Dried Fruits. Color; texture (chewiness); flavor (sweetness, acidity, sulfur residue, off flavors); moisture content; incidence of decay-causing pathogens; insect damage. The lower the moisture content the longer the postharvest-life.

TEMPERATURE & CONTROLLED ATMOSPHERE (CA)

Optimum Temperature

0-10°C (32-50°F); the lower the temperature the longer the storage-life. Some products can be stored frozen at -18°C (0°F) for a year or longer and remain in good condition

Optimum Relative Humidity

55-70% depending on the moisture content of the products (ranging from 2 to 20%); Equilibrium relative humidity should be identified and used to maximize storage-life. Packaging in moisture-proof containers is recommended.

Rates of Respiration

Very low [>1 ml/kg×hr at 10°C (50°F)] due to the reduced water content of the products and the effects of heat on the living status of the tissues.

To calculate heat production, multiply ml CO₂ / kg · hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.

Rates of Ethylene Production

None

Responses to Ethylene

None

Responses to Controlled Atmosphere (CA)

Oxygen levels below 1% are very effective in delaying rancidity, staleness, and other deterioration symptoms. Either oxygen levels below 0.5% (balance nitrogen) and/ or carbon dioxide levels above 80% in air can be effective in controlling stored-product insects and may provide an alternative to chemical fumigation. Packaging using vacuum or nitrogen flushing to exclude oxygen is recommended to maintain product quality.