Originating from Central America, with a natural range extending from Mexico to Panama, the Papaya or Paw Paw is nowadays cultivated around the world for its fruit, which are mostly eaten ripe but are sometimes used green in salads and chutneys.
Botanically, Papaya is a large herb lacking hard, woody stems. Instead, it develops an upright, unbranched semi-woody trunk with a hollow centre. Growing up to 8 m (26 ft) tall, though much shorter in the cooler parts of its range, the trunk is green when young, grey-brown when mature, smooth, except for leaf-scars, and is topped by a compact crown of very large leaves. On wounding, it yields a sticky white latex, as do all parts of the plant, including the green or unripe fruit.
Leaves deeply lobed, up to 60 cm (2 ft) long and almost as wide, dull dark green on top, pale green underneath, and attach to the trunk with a long, hollow leaf-stalk. Arranged along the top of the trunk, they remain on the plant for four to six months before they die-back and fall to the ground.
Flowers tube-shaped when formed, opening into five waxy-white petals and with male and female flowers either on separate plants or the same plant, though some varieties come with perfect flowers (having male and female parts). On plants bearing only male flowers, the flowers are in pendant clusters up to 1.5 m (5 ft) long. On all other plants, the flowers arise solitary, or in two or threes at the leaf axis. They come into bloom without seasonal influence, about four to six months after planting.
The fertilised flowers are followed by, depending on the type and variety, fruit that are roundish, pear-shaped, oval or elongated-oval. All have thin skin that is dull dark green when young, becoming orange-yellow when ripe and range greatly in size and weight, in length from 15 to 50 cm (6 to 20 in) and in weight from 0.5 kg to 7 kg (1 to 15 lbs) or more. They ripen in progression from the lowest fruit to those higher up on the trunk and are usually harvested when the skin is half green and half orange-yellow.
After harvesting, the fruit is stored for a few days. Over this time, the skin where green becomes orange-yellow and the fruit when fully ripe becomes soft to the touch, which signal its readiness for eating. The thin skin is easily peeled away revealing soft, aromatic, smooth, almost buttery-textured, orange-yellow to deep-orange pulp. At the centre of the fruit is a hollow cavity studded with small, round, brown-black seed.
There are many Papaya varieties, differing in plant size, fruit shape, fruit size, as well as pulp colour, flavour and degree of sweetness.
Papaya is normally eaten when the skin is fully coloured and the fruit is ripe and soft. To prepare the fruit for eating, the skin is usually peeled away, the seed removed and the soft pulp sliced or cubed. It is eaten as is, or is incorporated in fruit salads and desserts. In some regions, a fine grating of nutmeg or squeeze of lime juice is added to complement the flavour, which is sweet and aromatic. Alternately, the whole fruit is cut in half with the skin left on and the pulp, after scooping out the seed, is eaten with a spoon.
In Thailand and Vietnam, the green fruit are made into a popular salad known (unsurprisingly) as Green Papaya or Green Paw Paw salad. To make the salad, firm, fully-formed green fruit are peeled and the pulp finely shredded into long, thin strips. The strips are then combined with chili peppers, tomatoes, string beans, garlic and dried shrimp, usually by pounding them together in a mortar. To finish the salad, the pounded ingredients are dressed with a mixture of lime juice, fish sauce and palm sugar, and then topped with crushed peanuts.
Papain, a commercially important enzyme valued by the food, pharmaceutical and textile industries, is obtained from the latex. It has protein digesting action and is used as a meat tenderiser, as a clarifying agent to remove the protein haze in beer (and other bottled beverages), and in baking to break down gluten protein. It is also used in medicines and ointments to promote wound healing, and in textiles for de-gumming silk.
Papain is harvested from the green fruit while they are still on the plant, by wounding them with shallow, longitudinal incisions and then collecting the latex as it drips and falls. The is done early in the morning when the yields and enzyme activity are at their highest. New incisions are made every three to five days, as long as the fruit remains green.
After the latex is collected, it is spread thinly on trays and allowed to dry in the sun, or in a dryer, until the moisture level reduces to 5 to 8%. At the same time, care is taken to ensure the drying temperature does not exceed 40 °C (104 °F), as this will reduce the activity of the enzyme. Once dried, papain has a shelf-life of many months and is an off-white to greyish powder with a fine granular texture similar to semolina. It readily absorbs moisture, so needs to be stored in moisture-proof environment.
Papaya plants yield on average 140 to 225 grams (5 to 8 ounces) of dried papain per year, which roughly equates to 168 kg per hectare (150 lbs per acre).
The leaves and young fruit also contain good amounts of papain and are also used to tenderise meat. Wrapping tough pieces of meat in the leaves a few hours before cooking greatly reduces the toughness, as does adding the fruit to stews and casseroles. Only very young fruit are used, too young to have any seed, and generally only one fruit is needed per pot. Cut into halves or quarters, the pieces are added skin-on to the pot at the start of the
Ripe papaya pulp contains high levels of Vitamins A, B1 (Thiamine), B2 (Riboflavin), B3 (Niacin) and C (Ascorbic acid), as well as calcium.
The ripe pulp is also considered an aid to digestion, on account of its papain content. Papain being a digestive enzyme able to break-down the proteins in foods. For this reason, it is sometimes referred to as vegetable pepsin. It is used in chewing gum, as well as in preparing invalid and young children's food.
Grows naturally and produces sweet, flavoursome fruit in humid subtropical and tropical climates, generally frost-free areas with annual lows of 12 to 25 °C, annual highs of 22 to 35 °C, annual rainfall of 1200 to 3500 mm and a dry season of 5 months or less, extending to 8 months with irrigation.
In the cooler parts of its of its range, Papaya plants benefit from being planted close to a sun-facing wall, so that the wall will radiate heat, especially over the coldest days and nights. Without enough warmth, the plant may fail to flower and fruit, produce tasteless fruit, or become diseased and die. This practice is recommended for areas where the average low of the coldest month falls below 10 °C (50 °F).
New plants can be started from seed or cuttings. However, the risk of using seed is that cross-pollination may have occurred, and the desired characteristics may not have been passed on. For this reason, it is best to source seed only from hermaphrodite plants that have self-pollinated or that have been pollinated by another hermaphrodite plant.
Seedlings reproduced from hermaphrodite plants usually results in about two-thirds of the seedlings being hermaphrodite and one-third being female. By contrast, female-only plants only produce unisex seedlings, normally at a ratio one male to every female (1:1).
Because papaya plants are normally non-branching, cuttings have to be taken from the main stem or trunk. To obtain cuttings, the trunk on mature plants is divided into slender sections around 30 cm (1 ft) long and 5 cm (2 in) in diameter. These are then dipped in a fungicide bath and the rooting end in a rooting hormone. They are then planted in a free-draining potting mix, where most will strike roots within two to three months.
Performs best on free-draining loam, loamy-sand and sandy-loam soils of a moderately acid to alkaline nature, generally with a pH of 4.5 to 8.0, and on sites with full sun exposure.
Papaya plants start producing harvestable fruit about nine months after planting (though the 'Solo' variety may take up to eighteen months to do so) and continue to produce fruit for up to two years after that. Yields in commercial plantations average around 25,000 kgs per hectare (22,000 lbs per acre) per year, though yields of up to 85,000 kgs per hectare (76,000 lbs per acre) have been reported.
Papaya is recorded as having escaped cultivation in Australia, but the does not appear to be any record of it anywhere as a serious weed. It is assessed as a low weed risk species for Hawaii, by the Hawaii Pacific Weed Risk Assessment project (HPWRA).
The latex is extremely irritating to the eyes.
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