Bringing Science to Life through Real World Stories

Saturday, February 2, 2013

Science at Home: How to Ripen Fruit Quickly

Banana, Pear, and Golden Delicious Apple  ready to eat

Science at Home.
Photo from my own kitchen. 







Have some pears or apples that aren't quite ripe enough to eat? If you have a banana handy, use this simple trick to speed up the ripening process of the  fruit so you can enjoy it sooner.


Experiment:

Put a banana and your other fruit in a plastic bag (not completely sealed) or a brown paper bag. Wait. How long it takes for the fruit to ripen will depend on how hard it was to start with. 

You can also use a ripe apple to ripen other fruits using the same process. This works well with peaches, plums, and other stone fruits when placed in a paper bag. 

How does it work? 

Even though the fruit has been picked, the cells within it are still alive! Starch in the fruit gradually converts to glucose , a sugar, when certain enzymes are present. If you've ever tried to eat a pear before it was ripe, you probably noticed that not only was it very hard but it also wasn't sweet. That's because the starch hadn't yet converted to sugar, which is part of what makes fruit taste so yummy. 

Ethylene is a gas that is made by some fruits, and it triggers the ripening process. Ethylene acts like an enzyme by speeding up the conversion of starch to sugar. Bananas make lots of ethylene as they ripen. The ethylene gas that comes out of the banana is trapped in the bag, exposing the other fruits to extra ethylene. The extra ethylene then triggers the ripening process for the pear and the apple. Apples also produce a lot of etylene, and that's why they can also be used to ripen other fruits.

This doesn't work for all fruits. Some fruits ripen by other processes, like grapes and cherries. 

What happens if fruit is exposed to too much ethylene?

Fruits that make ethylene  to trigger ripening do not stop making ethylene once the fruit is ripe. They will continue to make ethylene, and the fruit will continue to get softer and softer, with more and more sugar, and will eventually be rotten.


How do you like your banana?

Bananas have many levels of ripeness and people often disagree about which one tastes best. Some people like them slightly green, when they have a bit of sweetness but are still quite starchy. At the other extreme are people who love bananas with lots of dark brown spots. These bananas are much softer and very sweet. They may have bruises caused by the fruit getting injured, which causes the ripening process to be accelerated at those spots.  


Did you know?

Bananas are picked very green and shipped in containers pumped with ethylene gas. Supposedly some grocery stores also have chambers to ripen fruit with ethylene before putting it in the produce area for sale. The ripening process can be stopped during shipping by stopping the addition of ethylene to the shipping containers.

Other Resources:

This website has a nice diagram showing the chemicals that are involved as fruit turns from  being unripe to ripe. 
http://plantphys.info/plants_human/fruitgrowripe.shtml

A more detailed explanation of how ethylene contributes to the fruit ripening process.

http://postharvest.tfrec.wsu.edu/pages/PC2000F

Nice resource about the ripening process for many fruits from a company that makes machines that produce ethylene safely for container ripening. The banana section has a chart showing bananas at several stages of ripening.

http://ripening-fruit.com/banana

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