Science of Cooking: Why do bananas go brown in the fridge?

To celebrate the launch of my recent book, The Science of Cooking: Every question answered to give you the edge, published by DK Books, I am starting a special series of posts about food science. The book answers 160 commonly asked cooking questions, busts lots of culinary myths (no, don’t throw away the mussels that haven’t opened), and gives you lots of how-to and hands-on guides for shopping and cooking impressive dishes without pricey equipment.

Not wanting to spoil any of the surprises within the book itself, consider this series of titbits a something of a hour derves…

Why bananas go brown in the fridge (they aren’t ripening – you’re hurting them!)

Chilling injury of bananas after being left in fridge

You probably thought you were being smart when you put the banana in the fridge, didn’t you? Everyone knows that food lasts longer when chilled. But when you open the fridge door a day or two later – shock horror! Your vibrant yellow tropical fruit has been replaced by a muddy brown slug. So why on earth did that fruit ‘turn bad’ so quickly?

Yes, it is true that most foods last longer when refrigerated – bugs can’t grow as easily and the chemical ageing processes are slowed. But bananas aren’t like milk, cheese and butter – bananas are alive and they come from a place that was nice and hot.

Bananas are not evolved to cope with the decidedly nippy ambience of a 21st Century refrigerator. They suffer ‘chilling injury’ when kept in the cold, much like how you or I might get frostbite in the Antarctic. The chilled banana senses that it is under threat and activates its defensive processes. An enzyme is released within the cells of the skin (called PPO) that makes it turn blotchy and brown. As it happens, this is the same enzyme that makes a cut apple turn brown.

But fret not – your banana isn’t actually ripening when in the fridge (it’s only pretending). Only the skin is degrading and when you peel off that ugly, blotchy skin, you will discover a perfectly tasty banana.

Fancy learning more about the science of cooking? Get the book here.

Thanks for reading. Feel free to add your thoughts in the comments below.


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