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Bananas! They’ve got a long trip from harvest to table, and a lot of science goes into keeping them delicious. This episode was produced in collaboration with and sponsored by Emerson. http://www.emerson.com/ilovestem

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Sources:
http://www.fao.org/docrep/019/i3627e/i3627e.pdf
http://cwh.ucsc.edu/bananas/Site/Modern%20History%20of%20the%20Banana.html
http://postharvest.tfrec.wsu.edu/pages/PC2000F
https://books.google.com/books?id=Fv2VH9LGQqoC
http://pages.wustl.edu/ipgsa/ethylene
http://www.actahort.org/members/showpdf?booknrarnr=879_40
http://www.researchgate.net/profile/Ruey-Shin_Juang/publication/10908469_Adsorption_of_heavy_metals_from_water_using_banana_and_orange_peels/links/0046351c8e921e1686000000.pdf
http://news.nationalgeographic.com/news/2011/03/110311-water-pollution-lead-heavy-metal-banana-peel-innovation/
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This is not the first time we've talked about the strange and amazing science of bananas. Last time we talked about how all bananas in the grocery store are genetically identical to each other and how just one disease could wipe them all out.

But that's not even the whole story. There's also the science of getting bananas from somewhere very far away from Montana, for example, and not having them ripen on the way, but indeed arrive at the grocery store just in time for me to take them home, and put them in my smoothie. 

Every step of that process has to be carefully controlled. As recently as the mid-19th century, bananas in North America and Europe were more of a curiosity. An exotic fruit that you would occasionally find at a market. But by the start of the 20th century, bananas were becoming a pretty big industry - 6.4 million dollars in the United States alone - and these days it's valued in the billions. 

Every year around 13% of bananas produced in the world are shipped to other markets and in 2012, that added up to 16.5 million metric tons of bananas. That's around 50 times the weight of the Empire State Building. 

And all of this was made possible by the development of the cold storage and transport industry, and the invention of a special ship just for this particular fruit.

Yes, banana boats, they were actually things. The original banana boats were basically giant refrigerated ships. 

They're a thing because bananas are temperamental. Unlike rice or wheat, you can't store them for long periods of time, especially not at room temperature because they'll just ripen. But if it's too cold, the banana's cell walls start to break down. 

Vacuoles within the peel's cells release compounds called phenols which combine with enzymes floating around in the cell to form melanin. The flesh, though mushy, is still perfectly edible, but the peel thins, making the banana more susceptible to bruising and also darkens, which you just...don't want a brown banana. All in all, not the simplest food to transport thousands of kilometers by boat.

Around 1930, the first banana boats were invented. A fleet of fast, refrigerated ships that could be kept at the perfect temperature for bananas - around 13 degrees Celsius. And it wasn't long before scientists figured out how to control when and how bananas ripen, leading to the shipping process still used today. 

Bananas are harvested and shipped while they're still completely green. These days they travel on multi-purpose reefer ships or in reefer containers. "Reefer" is just short for refrigerated because these boats and boxes are designed to keep the bananas at exactly the right temperature and humidity. 

Sometimes the reefer containers will be set up so that the bananas ripen on the way over, otherwise they are sent to special ripening rooms when they arrive. Either way, it's a carefully controlled process. The containers or rooms are filled with ethylene, also called ethene. 

Ethylene is a simple organic molecule, just a two carbon chain with a double bond. You might recognize it as the one of the building blocks of plastic - polyethylene. 

But for a banana, it is a ripening hormone that will completely change the fruit's life. Normally bananas slowly produce this hormone on their own but during shipping when they're kept at 13 degrees they hold off on it. So ethylene can be used to artificially induce the ripening process and ripening rooms are filled with the stuff. 

Among other things, the ethylene tells the banana to produce two extra enzymes - amylase and pectinase. Amylase we have in our bodies, it's in our saliva and its job is to break starches down into sugars. It does this very same thing in the banana, which goes from starchy to sweet.

At the same time pectinase helps to soften the banana by turning protopectin, which helps give structure to cell walls, into the more soluble pectin. Other enzymes break down the green chlorophyll in the peel and the banana starts to turn yellow.

Most bananas aren't kept in the ripening rooms long enough to turn yellow though, usually they're in there just long enough to get to the lighter side of green and then sent off to be sold to you and me.

So go get one! Nom!

Thanks for watching this episode of SciShow which was sponsored by Emerson. If you wanna keep getting smarter with us, you can go to youtube.com/scishow and subscribe. 

(Outro music)