Harvesting and Handling
Harvesting at the correct time is essential to the production of quality apples. To ensure maximum storage life, apples should be harvested when mature but not yet fully ripe or overripe. If harvested before they have matured, apples will have poor eating quality, will be more susceptible to storage disorders such as scald, cork spot, and bitter pit, and may not ripen properly. Ripe fruit should be avoided because it will continue to ripen in storage, rapidly becoming too soft and mealy for sale. Firmness and the level of soluble solids in the apple are good indicators of maturity to use in determining picking time.
Quality consists of a combination of visual appearance, texture and flavour. Modern consumers demand impeccable appearance and optimum texture and firmness typical of the variety.
Apples are very susceptible to bruising and other forms of mechanical damage and therefore should not be handled any more than necessary. The effects of bruising and scuffing cannot be reversed. Damage from rough handling will accelerate deterioration, reducing the value of the product.
The degree of ripeness of apples can be determined by measuring the firmness of the pulp with a pressure tester (i.e. penetrometer with 11,3 mm plunger). The pressure can be read off in pounds (or kilograms). At the pre-climacteric stage, the firmness of most apple varieties is between 18 and 20 pounds (lbs). During ripening, the firmness decreases by approx. 5 pounds. Apples testing at <12 lbs will have little storage life remaining and should be sold at earliest convenience. Consumers demand apples that are crisp and crunchy. Other textural or flavour components are secondary.
Cooling and Storage
An apple continues to live and respire even after it is picked. Although respiration cannot be halted completely, the objective of postharvest cooling is to slow the process and thus increase storage life.
Even if apples are to be stored for only a short period, it is still very important that the field heat be removed from them as soon as possible. Rapid cooling will not injure the apples.
The higher the holding temperature, the greater the softening and respiration rate and the sooner the quality becomes unacceptable. Apples respire and degrade about twice as fast at 4°C as at 0°C. At 15°C they will respire and degrade more than six times faster. The optimum storage temperature for apples depends on the variety, but all are within the range from -1°C to +4°C.
Apples are moderately susceptible to freeze damage. Temperatures more than 1 or 2 degrees below freezing should be avoided. Chilling damage in apples is often consistent with internal breakdown. It occurs at temperatures of around 0°C (cultivar and exposure time dependent) and is not generally visible from the outside. However, upon cutting, parts of the fruit flesh appear brown/moist with a narrow zone of normal tissue immediately beneath the skin. Later the vascular strands may darken. In advanced stages, the skin becomes waterlogged and discolored.
Apples may suffer freezing injury whilst on the tree, in store or during transit. Exposure to freezing conditions tends to be more damaging to harvested fruits than to those still on the tree. After slight freezing, the skin may show irregular areas of brown discoloration. Internal freezing injury can initiate watersoaking, flesh-browning and/or discoloration of the vascular strands. Such symptoms are not diagnostic, however, since other disorders can produce a similar effect. Severely frozen flesh leaks on thawing, becoming soft and brown. After subsequent storage, cavities may develop in the affected tissue. Even in the absence of obvious symptoms, fruits which have been exposed to freezing temperatures are weakened and their storage life is shortened. The fruit softens and becomes mealy.
All varieties require a relative humidity from 90 to 95 percent to prevent shrivel. Maintaining the humidity within this range will reduce weight loss, but humidity near the saturation point (100 percent) will encourage the growth of bacteria and fungi. Some varieties of apples, such as Golden Delicious, can be held in plastic liners to keep the humidity at high levels.
Chilled apples that are suddenly transferred into warm air are likely to “sweat” – that is, water vapour in the air will condense on them. Sweating also occurs when the doors of a cold storage room are opened, allowing warm, moist air to enter. Sweating itself does not harm the fruit, but it causes wetting, which encourages the growth of fungi and bacteria. Chilled apples should not be allowed to warm and then be re-chilled. To prevent sweating, chilled apples should be allowed to warm gradually inside the storage area, if possible, before bringing them out into the open air.
Since apples are stored longer than many other types of produce, it is essential that both the storage rooms and containers be clean and sanitary.
Low O2 (below 1%) can result in alcoholic off-flavours. High CO2 (above 6% continuously or above 15% for 10 days or more) can result in CO2 injury. Relative humidity greater than 98% may cause skin cracking.
Alcohol formation, Alternaria rot, Alternaria Canker, Ammonia injury, Anthracnose, Aphids, Apple scab, Aspergilles rot, Bacterial blister spot, Bitter pit, Black rot, Blossom end rot, Blue mould, Brown heart, Brown rot, Bruising, Bulls eye rot, Canker, Carbon dioxide injury, Chilling/freezing injury, Core flush, Diphenylamine injury (DPA), Dry Eye rot, Flyspeck, Freezing injury, Frost injury, Fusarium, Grey mould rot, Hail injury, Heat injury, Insect damage, Internal breakdown, Jonathan spot, Low oxygen injury, Penicillium, Phytophthora, Powdery mildew, Rhizopus rot, Rust, Scab, Scald, Senescent blotch, Senescent breakdown, Sooty blotch, Sun scald, Superficial scald, Water core, White rot