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A Clementine is a mandarin orange hybrid. It was introduced into the United States in 1909 and to California growers in 1914. Since then 30,000 acres have been planted with these sweet, easily peeled oranges. According to an article by Cynthia David in the produce industry journal, "The Packer," clementines are the fastest growing fruit in the citrus category. Ripe clementines are naturally sweet. They neither ripen nor get sweeter after picking.
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Just before ripening, some fruits produce a burst of ethylene gas. Ethylene is a simple hydrocarbon gas that is produced inside the fruit and outgassed into the environment. In response to the ethylene, starch in the fruit is converted to sugar, making the fruit sweeter and reducing the mealiness. Pectin breaks down, making the fruit softer. Chlorophyll breaks down, changing the color of the fruit from green to red, blue or yellow. The organic molecules in the fruit break down and become more volatile, increasing the aroma. We experience all these changes as "ripening."
Tree vs. Counter
Some fruit, bananas and apples, for example, can ripen after they are picked. These fruits are called "climacteric." What makes them different from other fruits is the ability to produce ethylene. A green banana left on the counter will continue to produce ethylene even though it has not been on the tree for some time. The ethylene will cause it to turn yellow and become softer and sweeter. Other fruits, peaches and plums, for example, produce only small amounts of ethylene. These fruits will become softer and less green after picking but they will not become sweeter. Still other fruits, non-climacteric fruits, don't produce ethylene gas. These fruits, strawberries and cherries for example, must ripen on the tree because they won't ripen on the counter.
Oranges, including clementines, are non-climacteric. The process of non-climacteric ripening is not as well-understood as climacteric ripening. What we do know is that oranges turn orange, soften and become juicy on the tree. If they are left on the tree for a while after they turn orange, they will become sweeter with time. Once an orange or a clementine is picked, however, it will not ripen further. It may become softer as it rots, but the sugars will not develop and quality of the fruit will not improve.
It is possible for an clementine, or any other kind of orange, to be fully ripe but to still have green patches on its skin. In other words, the orange can be soft and sweet and it can smell and taste like a fully ripe orange while being partly green. Because consumers are unaccustomed to their produce being ripe and green at the same time, growers often "degreen" citrus using synthetic ethylene gas. Green citrus fruit is placed in a chamber. Ethylene is pumped in. The skin of green oranges turns orange in response. The fruit, however, is not ripening in the strictest sense of the term. If an unripe orange is exposed to ethylene, it won't get softer or sweeter though it may change color. Moreover, oranges by nature don't ripen using ethylene.
- The Packer: With Clementines, Big Sales Come in Small Packages
The clementine craze continues to sweep the U.S., with no end in sight to the appeal of the small easy-peel orange.
- University of California, Riverside: Citrus Degreening
- University of California, Riverside: The History of Clementines
- Fruit Share: Ripening and Storage
- Quisqualis: Climacteric and Non-climacteric Fruit List
List of Rare Fruit and uncommon fruit anf their Climacteric or Non climacteric characteristics