Ripening is a process in fruits that causes them to become more palatable. In general, a fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level does not make the fruit seem tarter, which can lead to the misunderstanding that the riper the fruit the sweeter. This curious fact is attributed to the Brix-Acid Ratio.
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Ripening agents speed up the ripening process.
They allow many fruits to be picked prior to full ripening, which is useful, since ripened fruits do not ship well. For example, bananas are picked when green and artificially ripened after shipment by being gassed with ethylene.[1] A similar method used in parts of Asia is to put a plastic cover over a bed of slightly green-harvested mangos and a few small open containers of clumps of calcium carbide. The moisture in the air reacts with the calcium carbide to release the gas acetylene (ethyne), which has the same effect as ethylene. Ethylene is not emitted by the plant naturally, and cannot activate the ripening of nearby fruits, rather, it is used as a hormone within the plant.
Calcium carbide is used for ripening fruit artificially in some countries. Since industrial-grade calcium carbide may contain traces of arsenic and phosphorus, the use of this chemical for this purpose is illegal in most countries. Calcium carbide, once dissolved in water, produces acetylene,[2] which acts as an artificial ripening agent. Acetylene is believed to affect the nervous system by reducing the oxygen supply to the brain. Agricultural industry PR claims that acetylene is not sufficiently reactive to affect consumers.
Catalytic generators are used to produce ethylene gas simply and safely. Ethylene sensors can be used to precisely control the amount of gas.
Covered fruit ripening bowls are commercially available.[3] The manufacturers claim the bowls increase the amount of ethylene and carbon dioxide gases around the fruit, which promotes ripening.
Climacteric fruits are able to continue ripening after being picked, a process accelerated by ethylene gas. Non-climacteric fruits can ripen only on the plant and thus have a short shelf life if harvested when they are ripe.
Iodine (I) can be used to determine whether fruit is ripening or rotting by showing whether the starch in the fruit has turned into sugar. For example, a drop of iodine on a slightly rotten part (not the skin) of an apple will turn a dark-blue or black color, since starch is present. If the iodine is applied and takes 2-3 seconds to turn blue/black, then the process has begun but is not yet complete. If the iodine stays yellow, then most of the starch has been converted to sugar. [4]