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Ripening is a process in fruit that causes them to become more edible. In general, fruits get sweeter , less acidic, less green and softer as they ripen.

Stages of a plant's life, like a human's, are influenced by hormones. These are often connected to pollination. If too few seeds in a multiseeded fruit are formed (by fertilization of the ovules), the flesh of the fruit may not develop in some areas, and ripening will be retarded or prevented. Fruit growers increasingly monitor seed ratios in forming and/or mature fruit and adjust pollination management accordingly.

Shortage of pollinators can be an unrecognized factor in poor ripening of fruit. In a test in the Rio Grande valley of Texas, increasing the number of beehives in cantaloupes by a factor of about 2 1/2, increased the total crop by almost 7 tons per acre (1.6 kg/m²), mostly due to increased sugar content in the fruit.

An important plant hormone involved with ripening is the chemical ethylene. Ethylene is a gas created by plants from the amino acid methionine, and can easily be created synthetically. Ethylene causes increased levels of certain enzymes in the fruit. These enzymes include:

  • amylase, which breaks down starch to produce simple sugars.
  • pectinase breaks down pectin, the substance that keeps fruit hard.

Many fruits are picked prior to full ripening, because ripened fruits do not ship well. For example bananas are picked green, and then gassed with ethylene after shipment, so they can be artificially ripened. It is also possible to speed ripening at home. For example, kiwifruit are often slow to finish ripening, and ripening can be hastened by placing the fruit in a bag with an apple, which gives off natural ethylene gas.

Ethylene gas can also cause damage. If apples are stored with potatoes that have not been treated to prevent sprouting, the gas given off by the apples will cause the potatoes to sprout wildly.

Other enzymes break down the green pigment chlorophyll, which is replaced by other coloured pigments such as blue, yellow or red.

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