Thursday 7 July 2011

Bags o' Bananas

Bananas. Perfectly lined up along a windowsill on a beautiful sunny day. My flat mate was trying to induce a faster rate of ripening among them (my other flatmate makes super good chocolate-chip banana cake which requires ripe, going on rotting, bananas). 

The Banana Ripening Process
http://www.gettingrerooted.com/wp-uploads/geri//2010/01/banana_ripeningchart.jpg

Whilst this experiment is very clever; relying on sunlight and temperature to speed ripening, it quickly became apparent to me that’s probably not the way to do it.

I’ve always stored my bananas separately from my other fruit because it’s been proven bananas have a very high level of ethylene. Ethylene is a plant hormone known to induce senescence (fruit ripening, leaf death etc). So by keeping my bananas separate from my other fruit, I was preventing these from being ripened too quickly.

So then I thought, can the high levels of ethylene bananas produce be turned against them? I suggested the idea of enclosing the bananas and effectively trapping them amongst their own ethylene. And hey presto, the next day, super ripe bananas!

Bananas are often manipulated into ripening slower or faster by shops, and also at home. Now purchasable are ‘Banana bags’ a way to slow down the ripening process by storing them in the fridge. Claiming to keep bananas fresh for 2 weeks the bag works by insulating the fruit to prevent flesh over-ripening while keeping skin warm enough to prevent blackening. 

The Banana Bag
http://www.lakeland.co.uk/12159/Banana-Bag

While at the other end of the spectrum, supermarkets use ripening rooms; bananas are picked green and are kept at 15-17oc (a low temperature will chill fruit and prevent ripening and a high temperature will increase ripening too much) and subjected to 0.01-0.04% ethylene in an enclosed room for 24 hours. The bananas are then subjected to carbon dioxide in the same conditions (minus ethylene) for 4 days. Banana temperature during this process can increase to as high as 32oC.

In summary, the bag works because it subjects bananas to higher ethylene concentrations than if they were exposed to air, and it also maintains a higher temperature which speeds ripening to the point of almost rotting. The chocolate chip banana cake was scrumptious too
!

More info at 
http://www.hse.gov.uk/lau/lacs/31-2.htm
http://www.advancedripening.com/
http://www.catalyticgenerators.com/banriptip.html

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