I occasionally bring a banana to work. Today, as a matter of fact. This particular banana was sitting in my kitchen in my fruit basket for a few days, still yellow, couple dark spots, pretty firm.
I arrive in my office and set it on the credenza and in a half day it’s now turning somewhat black already. I’ve seen this happen before. Is there any logical reason?
I’m willing to bet that the rest of the bunch of bananas I left at home will still be mostly yellow when I return.
I imagine it’s going to be very difficult to get a factual answer, rather than an opinion, especially without knowing much about the conditions of your office vs. your home. Temperature differences? A higher concentration of ethylene gas in your office building?
Indivudual bananas ripen faster than the bunch due to an increase open surface area of the torn off end that allows the ethylene in the banana to be released faster. Wrapping the open end of the indivdual banana or the bunch will delay ripening.
Could be the ethylene gas effect. Ambient temperatures of home and office generally vary by 0.5 to 1 degree at the most. Thank you!
Yes. I saw this trick on TikTok, and it works great. Cover the end of the bunch (or solitary banana) where it’s been cut off the stalk or bunch, and it lasts a lot longer. (I also moisten the cut area before wrapping it in a piece of saran wrap and tightened down with an elastic). If I had to guess, the issues involved for the OP would be higher temperature and low humidity at the office.
Let us know how the home bananas look when you get back.
This bugged me for years too. So I asked the guy at the grocery why all the bananas in the boxes were green, but they turned brown as soon as I put them in my shopping cart! He said it was exposure to air and heat, they were jam packed together in the boxes and kept in a cool place in the store.
The air seems to be the critical part. Now, as soon as I get home I put the 'naners in my kitchen cabinet and they last a lot longer that way. That’s where I keep the 'maters now too. You could keep them in the fridge, but mine get weird when I do that. Probably too cold. Sometimes I don’t want a whole banana, so I peel the skin down to the level I want to eat, fold it over and keep it on the kitchen cabinet. It doesn’t get weird like in the fridge, and will still be fine the next day.
I’ve fought this battle for years as well. I’ve tried many of the tricks (wrapping the ends, putting the bunch in the fridge, etc.) to no avail. But I’ve not tried putting the 'naners in a cabinet behind a closed door. If I can find room in a cabinet, I will try that. Thanks for the tip!
I vaguely recall something from decades ago saying that bananas were usually shipped with a nitrogen atmosphere and this slowed the ripening.
BTW, for anyone who has not visited the tropics - fresh picked ripe bananas are so much better than North American store-bought. Sweeter. I was told this by a lady I worked with who was from the Caribbean, and when I dd visit places where bananas were local, found it to be very true.
Bananas at home still pretty much the same. Next time I take one to work I will try putting it in a desk drawer and see if it makes any difference. Thanks!
Maybe also some trauma from the trip between home and work? Bouncing around in the car, jostling in the lunch bag, getting beaten around by other foodstuffs. Then of course the mental anguish of being dragged to the office and not even being introduced to the staff or being able to contribute in any meaningful way. 
Not necessarily. I found this:
Too high a temperature destroys enzymes, and too low a temperature can break down the cell walls of the fruit so the contents mix and the fruit oxidizes, browns and softens abnormally. The optimum temperature and humidity conditions for ripening are 62 to 68 degrees Fahrenheit and 90 to 95 percent relative humidity
It would be very unlikely that the air in his office is exactly the same as his air at home. I’ve experienced the same phenomenon. I always bring two bananas to work but sometimes eat only one, so one remains here. It doesn’t ripen at exactly the same rate as the ones I have at home even though it is from the same batch.
I just thought the same thing about 15 minutes ago when I ate my banana at work. I eat a banana every morning at work so I bring enough for the week on Mondays. When I bring them, they are usually still attached to each other. The rest of the bunch, usually still attached, are at home on the kitchen counter. The work bananas are always riper than the ones at home. I wonder if florescent lights have anything to do with it. I know house plants do a lot better in my office than at home.
Despite this being the FQ forum, I’ll add the anecdotal suggestion that simply the extra handling of the banana in transit could be the cause. I sometimes take a banana from the kitchen to my home office as part of my lunch, putting it on a plate jammed against other items, moving it off the plate onto the desk, likely moving it again to make space for something on the desk, etc. – and then sometimes not actually eating it for another day or so. And a banana that has been down that road is always in worse shape (browner, softer) than its sibling bananas sitting quietly two rooms away in the same house.
True, though it’s likely the office is much dryer than home, at least in the winter time, which would suggest slower ripening.
What I’ve noticed using the saran wrap of the cut area on top - it does take longer to go leopard and then full on brown. While working it’s way to leopard territory, the skin gets very much thinner and softer (again, takes longer) just like as happens uncovered - but the edible part inside does not get as mushy and soft anywhere nearly as fast as when uncovered.