Avocado
Product Care

Harvest Maturity

Avocado Post-harvest Handling and Market Preparation Information Sheet (1.24MB)

The flowering period in avocados ranges from about 4 to 14 weeks, depending on cultivar and environmental conditions. Therefore, fruits from the same tree will vary in maturity dates. Determination of the correct harvest time is important because it affects the fruit quality and market life. It is important to pick the fruit when mature, as immature fruits will shrivel and not ripen properly. Determining the appropriate harvest maturity may be difficult and experience is important. Fruit of some avocado cultivars, particularly of the West Indian race, fall from the tree when physiologically mature and must be picked prior to fruit drop. In cultivars from the Guatemalan race and its hybrids, the fruits remain attached to the tree for as long as three or four months after physiological maturity has been reached. Avocados generally do not ripen while they are attached to the tree. Fruits are still hard when mature and ripen only after being picked.

Several indices may be used to determine avocado fruit maturity. In Guyana, the fruit is considered sufficiently mature for harvest when it reaches a specified calendar date (i.e. days after full bloom) and weight or size. The specific dates, weights, and sizes used to determine maturity vary by variety. Mature fruits are usually picked at weekly intervals over a period of a month or more, the largest fruits being selected each time.

The outer waxy surface of the avocado changes appearance upon fruit maturity. Smoothness of the skin is a reliable indicator of maturity in most varieties. As fruit approach maturity, they develop a smoother skin surface. Also, the glossiness or shine of the fruit surface becomes duller as the fruit reaches maturity.

External colour can be used as a maturity index. The skin colour of many cultivars changes from green to light green with maturity. Reddish streaks may also appear at the stem end of certain deep green skinned cultivars when the fruit becomes mature.

Internally, the seedcoat of mature fruit turns brown with maturity. Also, in some loose-seeded cultivars, mature fruit produce a hollow sound when tapped.

Oil content is used as a maturity index for those cultivars high in oil. A minimum of 8% oil is used as a maturity index for Hass avocados in California. However, oil content is not used for the cultivars grown in Guyana, since they are relatively low in oil content. The high oil containing cultivars (i.e. >18%) are not adapted to Guyanese growing conditions. Avocado cultivars grown in Guyana contain between 3% to 15% oil.

Dry matter is also used as an index of maturity for certain cultivars. A strong correlation exists between the percentage of oil and the dry matter content. The dry matter is determined by drying 10 gm (.4 oz) of chopped fruit tissue in a microwave oven for 5 minutes.
Avocado fruit are attached to the tree by a stem (pedicel) that changes in appearance as the fruit matures. The area of the stem nearest the fruit changes in colour from green to brown or black when the fruit is mature. This colour change signals the formation of an abscission layer in the stem indicating the fruit is mature and ready for harvest.

Harvest Method

Harvest carefully as even small cuts, scratches and abrasions can spoil the appearance of the fruit and lead to decay. Mechanical damage occurring during harvesting cannot normally be seen until fruits begin to ripen or after long-term storage. Bruising and puncturing result in localized softening and the development of microbial decay and secondary microbial infection. Fruits should never be pulled off the tree since the pedicel needs to remain attached. The use of gloves reduces the likelihood of mechanical damage during harvesting and field handling. Only mature fruits should be harvested for export. Immature fruits will shrivel and fail to ripen.

When the fruit can be reached from the ground or with a ladder, it should be removed from the tree with clippers, leaving about 1 cm (.4 in) of the pedicel (stem) attached. Fruits may be placed into a soft canvas-picking bag strapped around the waist (Figure 1) or placed directly into a field crate.

Where fruit cannot be reached by standing or climbing, picking poles should be used (Figure 2). Picking poles typically have a clipper or cutter bar attached at the end with a catching bag below (Figure 3). The bag should be shallow and made from cotton or soft canvas to prevent mechanical damage to the fruit during harvesting. Cutting edges should be kept sharpened and the catching bag should be relatively small. The picking pole can be made by hand and the collection bag can be sewn from canvas. The hoop used as the basket rim can be fashioned from steel tubing or thick wire.

Harvesting should be carried out on the day prior to, or on the day of shipment. Field grading should be done at the time of picking to separate the cracked, split, insect damaged or diseased fruit from the sound marketable fruit.

Field Containers

After harvest, the avocado fruit should be carefully transferred from the canvas-picking bag into a field crate. Fruits should be gently put into the field containers to avoid mechanical damage. The fruit should not be placed on the ground. Plastic or wooden crates that hold about 25 lb (11 kg) of fruit are the preferred type of field container. The field containers should not be overfilled and they should be strong and capable of being stacked. The field containers should be lined with paper or foam to protect the fruit surface from abrasion. The containers of fruit should be kept in a shaded area and protected from rain. Exposure to the sun will raise the fruit temperature, which hastens ripening and shortens shelf life.

Mesh or canvas sacks are not recommended for use as field containers. They provide little or no protection to the fruit and cannot be stacked without imparting damage to the fruit during transport from the field to the packing facility.

Preparation for Market

The provision of shade during the packing operations is extremely important. Shade can be created using palm leaf fronds; a plastic mesh or canvas sheet hung from temporary poles, or via a permanent roofed structure. The first step in the packing process is to separate the unmarketable fruit that have been damaged, decayed, malformed, and scarred (e.g. fruit with growth cracks and healed abrasion injuries) from the sound marketable fruit. The fruit should then be cleaned, graded/sorted, and packed.

Cleaning

Most avocado fruit can be cleaned by gently wiping the surface with a clean soft cotton cloth or gloves. It may be necessary to use a moist cloth if the dirt particles or surface stains are difficult to remove. Moist cloths should periodically be dipped in a mild solution of chlorine (i.e. 150 ppm) to minimize the spread of disease. The stem stalk (pedicel) should be trimmed to 1 cm (.4 in) in length to reduce the risk of injury of puncturing adjacent fruit.

A postharvest fungicide treatment (overhead spray or dip) may assist in suppressing disease development. Effective treatments include 500 ppm thiabendazole or 2000 ppm Procloraz. However, importing country legislation should be checked before applying a postharvest fungicide. Hot water submersion of the fruits for 3 to 5 minutes at 50°C (122°F) may also help suppress disease development

Grading and Sorting

Avocados should be graded and sorted immediately following cleaning. Packinghouse grading is required to remove fruits not out-graded in the field or those damaged during transport from the field to the packinghouse. Fruits should be graded according to size and rejected for export if they are too small, have unhealed wounds or obvious mechanical damage, have excessive scarring or blemishes, have noticeable insect damage or decay, or if they have a loose seed. A high-quality avocado is mature, green or purple in colour; uniform in shape characteristic of the cultivar; appropriately sized, and free of mechanical damage, sunburn, wounds, insect damage, wind scarring, and decay (Figure 4). The flesh texture should be smooth and devoid of fibrous strings. The internal colour should be creamy or light green without flesh browning (Figure 5).

The desired characteristics of avocados for export are summarized in Table 1.

Table 1. Summary Specifications for Avocado Exports
Characteristics:	Clean, green or purple, firm, uniform in size and shape
Size:	Minimum weight 125 gm (4.4 oz) Maximum weight 660 gm (23 oz)
Counts:	Count 4: 780 to 1220 gm (28 to 43 oz) Count 6: 575 to 780 gm (20 to 28 oz) Count 8: 460 to 575 gm (16 to 20 oz) Count 10: 366 to 460 gm (13 to 16 oz) Count 12: 306 to 365 gm (11 to 13 oz) Count 14: 266 to 305 gm (9 to 11 oz) Count 16: 236 to 265 gm (8 to 9 oz)	Count 18: 211 to 235 gm (7.5 to 8.3 oz) Count 20: 191 to 210 gm (6.7 to 7.5 oz) Count 22: 171 to 190 gm (6 to 6.7 oz) Count 24: 156 to 170 gm (5.5 to 6 oz) Count 26: 146 to 155 gm (5 to 5.5 oz) Count 28: 136 to 145 gm (4.8 to 5 oz) Count 30: 125 to 135 gm (4.4 to 4.8 oz)
Condition:	Mature Free from mechanical damage Free from disease and insect presence and chilling damage Pedicel intact and no longer than one cm (.4 in).

Waxing

Waxing avocado fruit may help improve the surface appearance by adding shine and luster (Figure 6). Waxing also reduces weight loss and slightly delays ripening. In addition, waxing reduces the incidence of internal and external stem end rots. However, green-skinned cultivars may develop surface discolouration if the proper wax formulation and application methods are not used. A shellac or carnauba based food grade wax works well with avocadoes.

Packing

All the fruit within a carton should be approximately the same size and weight. Selection of uniform sized fruit to be put in each carton is done manually. For export, large fruit should be packed in single layers in strong fiberboard cartons with separators. A commonly used export carton has dimensions of 40 cm (27.5 in) long, 30 cm (12 in) wide, and 11 cm (4 in) high. It contains 4 kg (9 lb) net weight of fruit. Smaller fruit may be placed in larger fiberboard cartons with or without separators and packed in two or three layers. Each alternate fruit should be wrapped in tissue paper to reduce vibration injury and fruit scarring during transport (Figure 7). Shredded paper placed in the base of the carton also aids in reducing the level of damage during packing. A minimum bursting strength of 275 psi is necessary to ensure adequate carton strength during long distance transport. Carton labeling should follow import market requirements, but always includes exporter, importer, country of origin, product, variety, grade, count, and net weight. Lined wooden crates may be used for domestic marketing.

Postharvest Temperature Management

Postharvest temperature dramatically affects market life and the rate of ripening. The West Indian type avocado cultivars grown in Guyana should be held at 12°C to 13°C (54°F to 56°F) for maximum shelf life. The fruit is susceptible to chilling injury at temperatures below 12°C (54°F). The rate of ripening, fruit softening, and decay increases with temperature. Expected market life of fruit held at ambient temperature (i.e. 25°C to 30°C or 77°F to 86°F) will vary from 1 to 2 weeks, depending on harvest maturity.

Relative Humidity Management

The ideal storage relative humidity (RH) for avocadoes is between 90% to 95%. Weight loss and shrivel are significantly higher at low RH.

Ripening

Avocados generally do not ripen on the tree. Ripening involves flesh softening and a change of skin colour in some cultivars. The rate of ripening after harvest is determined by the harvest maturity of the fruit, temperature, and exposure to ethylene. West Indian type avocados ripen best at temperatures between 16°C to 24°C (60°F to 75°F). At higher temperatures, fruit ripen unevenly and develop off-flavours. Treatment with 100 ppm ethylene at 20°C (68°F) for 24 to 48 hours induces avocados to ripen in 3 to 6 days.

Early season mature fruits may take 10 to 12 days to ripen at 20°C (68°F), whereas mature fruit harvested late in the season may ripen in five to six days. Unripe avocadoes should not be stored with ethylene-producing crops if required in the firm unripe condition. Ripe (soft) avocados require very careful handling to minimize physical damage. Soft ripe fruit has a shelf life of only several days.

Transportation

Avocadoes can be shipped by air or sea. For sea shipment, fruits should be harvested the day prior to departure and cooled. A temperature of 13°C ± 1°C (55.5°F ± 34°F) and a 90% RH should be maintained inside the marine container. Avocados intended for export must be shipped in the firm mature stage in order to withstand the rigors of handling and transportation.

Principal Postharvest Diseases

Avocados are susceptible to several common postharvest fungal diseases, including Anthracnose, Stem-end rot, Fusarium rot, and Soft rot.

Anthracnose

Anthracnose, caused by the fungus Colletotrichum gleosporioides, is a serious postharvest disease of avocado fruit. The fungus does not develop until the fruit begins to ripen. Fruit lesions start as circular, slightly sunken, brown to black spots. These lesions enlarge rapidly under favorable conditions, often becoming conspicuously sunken with cracks radiating from the lesion center (Figure 8). The affected areas become covered with pinkish spore masses in later stages. The fungus can progress into the flesh of the avocado fruit, producing a brownish-black decay and rancid flavour, which eventually may involve a large portion of the fruit.

The Colletotrichum fungus is considered a weak pathogen and requires some type of wound to penetrate the avocado and subsequently cause disease. Mechanical damage, scab, and especially Cercospora spot lesions are known entry sites for the anthracnose fungus. Insects may also provide wound-infection sites.
Since all cultivars are susceptible, anthracnose control depends on good orchard sanitation and control of other diseases (especially Cercospora spot) and avoidance of cuts and bruises to the fruit in handling. Fruits showing any sign of anthracnose should not be packed in cartons with healthy fruit. Dipping the fruit in a 500 ppm solution of thiabendazole may also reduce the incidence of anthracnose. Cooling the fruit to 13°C (55.5°F) and maintaining that temperature during marketing will minimize anthracnose development.

Harvesting fruits in an immature condition can contribute to anthracnose appearance since the fungus may infect immature fruit and remain dormant, with subsequent invasion of the flesh through small cracks made during ripening or postharvest handling.

Stem End Rot

Stem end rot is caused by two different fungal organisms, Botryodiplodia theobromae and Dothiorella gregaria. Symptoms appears as an initial dark brown to black discolouration beginning at the stem end and advancing toward the blossom end, finally covering the entire fruit (Figure 9). Decay develops rapidly as the fruit softens. Stem end rot is usually only a problem with immature harvested fruit and can be prevented by harvesting fruit at the proper stage of maturity. Control measures used for anthracnose will also help minimize stem end rot.

Fusarium Rot

Fusarium rot is caused by several species of Fusarium. Infection usually takes place via the stem end or through injuries in the skin (Figure 10). This fungal disease accelerates the rate of softening and ripening. Recommended control measures are similar to those used for combating anthracnose.

Rhizopus Rot

Rhizopus rot is caused by the fungus Rhizopus stolonifer. It is characterized by rapid decay of ripe avocados with the formation of a coarse white mold on the fruit surface. Liquid may leak from the fruit and the odour is unpleasant. Infection is associated with wounds and can be significantly reduced by careful harvest and postharvest handling to minimize mechanical injuries.

Chilling Injury

Guyanese avocados are susceptible to chilling injury when kept at temperatures below 10°C (50°F). External symptoms of chilling injury include browning or blackening of the skin, pitting, and sunken lesions. Internal symptoms include browning around the vascular bundles and/or a general grayish-brown discolouration of the flesh (Figure11). Chilling injured fruit fail to ripen normally, develop off-flavours, and are highly susceptible to pathogen attack. The amount of chilling injury damage depends on the storage temperature, duration of exposure to chilling temperatures, cultivar, production area, and maturity-ripeness stage.