Ethylene gas accelerates the ripening process of a
banana, but why?
Ethylene produced naturally by the plant accelerates ripening and
maturation of the fruit.
Anthony Brach Ph.D.
Plants use ethylene (C2H4, also called ethene) as a hormone. It is a
very small, simple molecule that exists as a gas at biological
temperatures. Thus, when a plant releases ethylene, it diffuses quite
quickly in the air.
Different kinds of plants use ethylene differently; among the uses are
the promotion of fruit development and ripening, release of buds from
dormancy in springtime, stimulation of leaf and fruit abscission
(dropping), causing some plants to become female, stimulation of leaf
senescence, induction of flowering, etc.
Bananas use ethylene to stimulate fruit ripening. A bunch of bananas
will stay green for a long time until the ethylene concentration in the
air around them becomes high enough. When that happens, then they begin
ripening and they begin releasing more ethylene, which makes them ripen
faster and release more ethylene, etc. In this way, all of the bananas
will ripen very suddenly and simultaneously. Keeping bananas in a
plastic bag will make them ripen much more quickly than if you leave
them out in the open, because the plastic bag traps the ethylene and
thus makes its concentration rise more quickly.
Many other fruits - including apples and tomatoes, which are related to
bananas only very distantly - use the same mechanism. If one apple in a
barrel starts to ripen quickly (i.e. "goes bad"), it will cause all of
the surrounding apples to do likewise. One bad apple spoils the bunch.
Fruit distributors often take advantage of this effect by picking fruit
well before ripening and then shipping fruit to grocers while it is
still green. Then, just before delivery, the fruit is gassed with
ethylene to kick-start the ripening process. This helps make sure none
of the fruit will ripen too early, which would be problematic at the
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Update: June 2012