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I often see this technique suggested as a way to speed ripening. Why does it?

Also, is there any data available on how fast it ripens comparatively?

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5 Answers

up vote 27 down vote accepted

The ripening itself is caused by ethylene gas released by the food, which is trapped by any kind of bag.

As far as I know, there's nothing inherently special about a brown paper bag, other than the fact that it's porous and thus still allows some air to get in and out. Plastic ziplock bags have no ventilation, so they don't work nearly as well.

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Placing fruit in a bag will help hasten the ripening for only a few fruits. Most fruits will not ripen (ever) once they have been picked. The only fruits that ripen once they're picked are bananas, avocados, pears, mango, and kiwifruit. Ripeness in fruits is based on sugar content, not color, thus most tomatoes in grocery stores have no flavor because they were picked green and exposed to ethylene gas to induce color change. Tomatoes are what are known as a "climacteric fruit" which means they'll change appearance based on climactic conditions but they don't ripen. Yes, they continue to soften but that's simply the process of cell deterioration know as decomposition.

Some fruits such as peaches, plums, etc. will seem to develop more sweetness as they sit on the counter but that's because they're also losing moisture and the residual sugars are concentrating in the cell walls.

Placing fruit in a paper bag helps to concentrate the levels of ethylene gas which is what helps induce the ripening of the above mentioned fruits (bananas/avocados, etc.). In fact, avocados and pears must be picked in order to ripen. Pears that are left on the tree will simply rot. As mentioned previously... brown paper bags used to be something everyone had around their house so it was a commmon item before the switch to plastic bags.

Have you ever noticed some people like red bell peppers and not green ones? The reason is due to ripeness.

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If you're going to make the statement that only bananas, avocados, pears, mango and kiwi ripen after picking you should provide some reference. Everyday experience, a quick google and check of reputable sources, and common sense indicate otherwise. –  hobodave Jul 17 '10 at 4:41
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@Hobodave: Reference re: Ripening "On Food & Cooking" by Harold McGee, Scribner, revised edition 2004, Chapter 7, page 350-353. Page: 353 "nonclimacteric fruits like pineapples, citrus fruits, most berries, and melons don't store starch or improve markedly after harvest, so their quiality depends on how far they had ripened on the plant." "With just a few exceptions (pears, avocados, kiwis, bananas), even climacteric fruits will be much better if they're allowed to ripen on the plant, from which they can continue to accumulate the raw materials of flavor until the harvest." –  Darin Sehnert Jul 17 '10 at 4:51
    
Interesting. I'm finding conflicting information all over the place. seasonalcooking.suite101.com/article.cfm/fruit_ripening_stages has a list of fruits that fall into different categories (it has it's own references). Yet lancaster.unl.edu/food/ciqaa.shtml seems to conflict with the first source by saying peaches and apricots ripen. :-\ –  hobodave Jul 17 '10 at 5:02
    
I guess it's just one of those things that involve a bit of hand waving even by experts. :) I'll remove my down vote, thanks for providing the reference. –  hobodave Jul 17 '10 at 5:07
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Re: the listing showing Apricots as ripening.. "On Food & Cooking" 2004 edition, p. 352 Howard McGee offers a chart highlighting Fruits and their potential for improvement after harvest. the only ones that he lists for improving on sweetness are: Apples, pears, Banana, Mango, Kiwi but he does list others as improving in Aroma and Softness (which again softness is part of deterioration anyway). Among those listed as improving in aroma and softness: apricot, peach, plum, blueberry, raspberry, cantaloupe, honeydew, cherimoya, guava, papaya, passionfruit, avocado, persimmon, tomato. –  Darin Sehnert Jul 17 '10 at 5:19
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The secret is that the fruit produces ethylene (a hormone found in plants), and ethylene promotes ripening. By placing fruit in a paper bag the ethylene collects (rather than dispersing in the room), increasing the concentration around the fruit and speeding ripening. About.com has an interesting article on ethylene and fruit ripening called Fruit Ripening and Ethylene Experiment.

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This part I knew. But, why brown? Why paper? Why not a white paper bag? or a plastic bag? or a bread box? –  hobodave Jul 9 '10 at 20:03
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As a clarification, paper bags are better than plastic because they allow some airflow. More info here - state.nj.us/jerseyfresh/howtoripen.htm –  Kiesa Jul 9 '10 at 20:06
    
To the best of my knowledge it's really just tradition. I've used cloth bags before as well. The keys are to keep the ethylene near the fruit, but not to seal it up too tightly (such as in a plastic bag) so that it can still breath and doesn't sweat. –  Guildencrantz Jul 9 '10 at 20:07
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@hobodave : white paper bags are more likely to be treated to make them smooth to the touch (I think they use clay?), which can make it less easy to allow air through. Also, brown paper bags used to be a pretty commonly available thing, before most grocery stores switched over to plastic bags. –  Joe Jul 13 '10 at 22:07
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More importantly, brown paper bags allow moisture to pass through, so you don't get condensation that will accerate mold growth. Just leave produce on your counter in a plastic bag and witness the flexible petri dish!

White would probably work if it is porous enough.

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I've never heard this, but ripening is usually sped up by various airborne chemicals functioning as plant hormones. This is why one bad apple will cause others to go bad - it is signalling them. So I suspect it is either a matter of enclosing the airborne chemicals, or that paper bags release some such chemical.

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