Climacteric fruits like mango and bananas are harvested while still at their hard green stage. They are more resistant to damage during handling, transport and storage before reaching selling areas. Doing it otherwise will incur lots of losses. Ripe fruits are soft and prone to damage.
Then most middlemen are responsible for ripening agricultural produce. There are two basic ways to do this. The natural method and the induced method. Natural method is simply letting the fruit ripen by itself. Fruits are producing ethylene – a substance that promotes ripening. Naturally ripen fruits taste better while those which ripen while still attached to tree branch are the best tasting. I bet you will agree!
However. Natural ripening has one major drawback. One container of mangoes will not ripen at the same time. Some are ripe and some are still green. Some parts are already yellow while other are still green. The same thing happen to bananas. All bananas in a bunch will not ripen naturally at the same time.
A uniformly ripe mangoes and bananas have nice appearance and therefore more appealing and salable. The induced ripening method is needed achieved it. Almost all fruits will ripen uniformly and at the same time after induced.
I am not expert when it comes to this field but my mom and dad are veterans. I always see how they do it. They used to sell large number of mangoes and bananas. The local term for this is pagkululob or pagkakalburo.
What they do?
1) The common container for doing this is the kaing (slotted bamboo basket). One small kaing is about the size of regular water pail.
2) Kaings are lined with wide plastic sheet (should be enough to cover the whole container). Then lined again with newspaper.
3) Calcium carbide (kalburo), about half of a closed fist, is wrapped with newspaper and placed in bottom.
4) Mangoes or bananas are then arrange carefully to container brim. When using a large container, another calcium carbide should also be placed in middle and top.
5) Cover the fruit file with newspaper and plastic. Let stand for 24 hours. Calcium carbide will react with moisture and produce acetylene gas. The substance is similar to ripening inducer, ethylene.
6) Unpack the fruits and allow another 24 hours before consumption. According to my mom and dad, eating the fruit immediately will cause lose bowel movement and vomiting.
update as of January 2018
Use of calcium carbide as ripening agent is discouraged worldwide. The released gas that induced ripening is toxic in high concentration. Harmful in low exposure. Nausea and vomiting are two of the symptoms.
So what my parents said has scientific basis. Allowing the treated fruits untouched for a while allows the exit of harmful acetylene gas.