The kiwifruit or Chinese gooseberry (sometimes shortened to kiwi) is the edible berry of a woody vine in the genus Actinidia. The most common cultivar group of kiwifruit ('Hayward') is oval, about the size of a large hen's egg (5–8 cm (2.0–3.1 in) in length and 4.5–5.5 cm (1.8–2.2 in) in diameter). It has a fibrous, dull greenish-brown skin and bright green or golden flesh with rows of tiny, black, edible seeds. The fruit has a soft texture and a sweet but unique flavor, and today is a commercial crop in several countries, such as Italy, New Zealand, Chile, Greece, and France.
Kiwifruit is native to north-central and eastern China. Cultivation of the fuzzy kiwifruit spread from China in the early 20th century to New Zealand, where the first commercial plantings occurred. Although cultivars were called by a variety of Chinese names, such as yang tao, meaning "strawberry peach", "Chinese gooseberry" (because of the flavor and color of the flesh) became commonplace as a name among growers in England and New Zealand during the early 20th Century and during World War II when the fruit was popular with American servicemen stationed in New Zealand. The fruit was exported to California using the names "Chinese gooseberry" and "melonette". In 1962, New Zealand growers began calling it "kiwifruit" to give it more market appeal, followed by a California-based importer also using the name, "kiwifruit", to introduce the fruit to the American market.
The genus Actinidia contains around 60 species. Though most kiwifruit are easily recognized as kiwifruit (due to basic shape) their fruit is quite variable. The skin of the fruit can vary in size, shape, hairiness, and color. The flesh can vary in color, juiciness, texture, and taste. Some fruits are unpalatable while others taste considerably better than the majority of the commercial varieties.
The most common kiwifruit is the fuzzy kiwifruit, from the species A. deliciosa. Other species that are commonly eaten include golden kiwifruit (A. chinensis), Chinese egg gooseberry (A. coriacea), baby kiwifruit (A. arguta), Arctic kiwifruit (A. kolomikta), red kiwifruit (A. melanandra), silver vine (A. polygama), purple kiwifruit (A. purpurea).
Almost all kiwifruit sold belong to a few cultivars of fuzzy kiwi (Actinidia deliciosa): 'Hayward', 'Blake', and 'Saanichton 12'. They have a fuzzy, dull-brown skin, and bright-green flesh. The familiar cultivar 'Hayward' was developed by Hayward Wright in Avondale, New Zealand, around 1924. It was initially grown in domestic gardens, but commercial planting began in the 1940s.
'Hayward' is the most commonly available cultivar in stores. It is a large, egg-shaped fruit with a sweet flavor. 'Saanichton 12', from British Columbia, is somewhat more rectangular than 'Hayward' and comparably sweet, but the inner core of the fruit can be tough. 'Blake' can self-pollinate, but it has a smaller, more oval fruit and the flavor is considered inferior.
The golden kiwifruit (Actinidia chinensis) has a smooth, bronze skin, with a beak shape at the stem attachment. Flesh color varies from bright green to a clear, intense yellow. This species is sweeter and more aromatic in flavor; the flavor is reminiscent of some subtropical fruit. Its short storage life currently limits its commercial potential. One of the most attractive varieties has a red 'iris' around the center of the fruit and yellow flesh outside. The yellow fruit fetches a higher market price and, being less hairy than the fuzzy kiwifruit, is more palatable for consumption without peeling.
Hort16A is a golden kiwifruit marketed worldwide in decreasing volumes because this variety suffered significant losses in New Zealand from late 2010 to 2013 due to the PSA bacterium. A new variety of golden kiwifruit, 'Gold3', has been found to be more disease-resistant and most growers have now grafted over to this variety. The Gold3 variety, marketed by Zespri as 'SunGold', is not quite as sweet as the previous Hort16A, with a hint of tanginess, and lacks the Hort16A's usually slightly pointy tip.
Kiwi berries are composed of three species of kiwifruit; hardy kiwi (Actinidia arguta), Arctic beauty (A. kolomikta), and silver vine (A. polygama). They are fast-growing, climbing vines, durable over their growing season. The fruits are edible berry- or grape-sized fruits similar to the fuzzy kiwifruit in taste and appearance, with thin, smooth skin. They are referred to as kiwi berry, baby kiwi, dessert kiwi, grape kiwi, or cocktail kiwi.
The cultivar 'Issai' is a hybrid of hardy kiwi and silver vine which can self-pollinate. Grown commercially because of its relatively large fruit, Issai is less hardy than most hardy kiwi.
Kiwifruit can be grown in most temperate climates with adequate summer heat. Where fuzzy kiwifruit (A. deliciosa) is not hardy, other species can be grown as substitutes.
Kiwifruit is commercially grown on sturdy support structures, as it can produce several tonnes per hectare, more than the rather weak vines can support. These are generally equipped with a watering system for irrigation and frost protection in the spring. Kiwifruit vines require vigorous pruning, similar to that of grapevines. Fruit is borne on one-year-old and older canes, but production declines as each cane ages. Canes should be pruned off and replaced after their third year.
Most of the plants require a male plant to pollinate a female plant for the female plant to produce fruit (dioecious). For a good yield of fruit, one male vine for every three to eight female vines is required. Other varieties can self pollinate, but they produce a greater and more reliable yield when pollinated by male kiwifruit vines.
Kiwifruit is notoriously difficult to pollinate, because the flowers are not very attractive to bees. Some producers blow collected pollen over the female flowers. Generally, the most successful approach, though, is saturation pollination, where the bee populations are made so large (by placing hives in the orchards at a concentration of about 8 hives per hectare) that bees are forced to use this flower because of intense competition for all flowers within flight distance.
Firm kiwifruit ripen after a few days to a week when stored at room temperature, but should not be kept in direct sunlight. Faster ripening occurs when placed in a paper bag with an apple, pear, or banana. Once a kiwifruit is ripe, however, it is preserved optimally when stored far from other fruits, as it is very sensitive to the ethylene gas they may emit, thereby tending to over-ripen even in the refrigerator. If stored appropriately, ripe kiwifruit normally keep for about one to two weeks.
Pests and diseases
Pseudomonas syringae actinidiae (PSA) was first identified in Japan in the 1980s. This bacterial strain has been controlled and managed successfully in orchards in Asia. In 1992, it was found in northern Italy. In 2007/2008, economic losses were observed, as a more virulent strain became more dominant (PSA V). In 2010 it was found in New Zealand's Bay of Plenty kiwifruit orchards in the North Island.
Scientists reported they had worked out the strain of PSA affecting kiwifruit from New Zealand, Italy, and Chile originated in China.
|Source: UN Food & Agriculture Organization|
Kiwifruit exports rapidly increased from the late 1960s to early 1970s in New Zealand. By 1976, exports exceeded the amount consumed domestically. Outside of Australasia, all New Zealand kiwifruits are now marketed under the brand-name label Zespri.
Over 70% of kiwifruit production is in Italy, New Zealand, and Chile. Italy produces roughly 10% more kiwifruit than New Zealand, and Chile produces 40% less. With these three main production centers, kiwifruit is produced for worldwide consumption roughly all year long.
In the 1980s, countries outside New Zealand began to export kiwifruit. In Italy, the infrastructure and techniques required to support grape production have been adapted to the kiwifruit. This, coupled with being very close to the European kiwifruit market, led to Italians becoming the leading producer of kiwifruit. The growing season of Italian kiwifruit does not overlap much with the New Zealand or the Chilean growing seasons, therefore direct competition between New Zealand or Chile was not much of a factor.
Although kiwifruit is a national fruit of China, until recently, China was not a major producing country of kiwifruit, as it was traditionally collected from the wild. In China, it is grown mainly in the mountainous area upstream of the Yangtze River, as well as Sichuan.
Raw kiwifruit is rich in the protein-dissolving enzyme actinidain (in the same family of thiol proteases as papain), which is commercially useful as a meat tenderizer. Actinidain also makes raw kiwifruit unsuitable for use in desserts containing milk or any other dairy products which are not going to be served within hours, because the enzyme soon begins to digest milk proteins. This applies to gelatin-based desserts, as well, as the actinidain will dissolve the proteins in gelatin very quickly, either liquifying the dessert, or preventing it from solidifying.
To overcome this effect, the United States Department of Agriculture suggests cooking the fruit for a few minutes before adding it to gelatin. Sliced kiwifruit has long been regularly used as a garnish atop whipped cream on the common New Zealand and Australian dessert, the pavlova. It can also be used in a variety of other savoury and sweet dishes.
The actinidain found in kiwifruit can be an allergen for some individuals. Specifically, people allergic to latex, bananas, papayas, or pineapples are likely to also be allergic to kiwifruit. The fruit also contains calcium oxalate crystals in the form of raphides. Reactions to these chemicals include sweating, tingling, and sore mouth or throat; swelling of the lips, tongue and face; rash; vomiting and abdominal pain, heartburn; and, in the most severe cases, breathing difficulties, wheezing, and collapse. The most common symptoms are unpleasant itching and soreness of the mouth, with the most common severe symptom being wheezing. Severe symptoms are most likely to occur in young children.
Kiwifruit is a rich source of vitamin C (1.5 times the United States DRI per 100 grams) and vitamin K, and a good source of dietary fiber and vitamin E. The fruit and skin contain flavonoids, actinidain, and adhered pollen, which may produce irritation in the mouth and throat of some allergic individuals.
Kiwifruit seed oil contains on average 62% alpha-linolenic acid, an omega-3 fatty acid. Usually a medium size kiwifruit provides about 46 calories, 0.3 g fat, 1 g protein, 11 g carbohydrates, and 2.6 g dietary fiber found partly in the edible skin. Kiwifruit is often reported to have mild laxative effects, due to its significant levels of dietary fiber.
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