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I bought a bag of potatoes and a hand of bananas on Sunday (from Costco) and just let them sit in the kitchen until Friday, when I noticed water oozing out of a few of the bananas.

Then, the next day, I found that a few thumb-sized spots on the potatoes had also become mushy and had a terrible smell. This ooze is pure white, feeling and looking like mashed potatoes (but I never cooked them), not the normal darkening I am used to in potato rot.

It's like something just spoiled these two produce products and cut short the full aging/ripening process after one week.

Why?

So, I focused on the potatoes, since they had the strangest spoilage, and went online to understand this. I could only find one match, which is also very recent (written just 1 month ago, but I believe the experience was 10 months ago) and even has a video of this mush.

That match suspects either "freezing injury" or "rot bacteria". I wonder if this bacteria is known to spread to bananas. Additionally, I wonder if "water droplets" left on the potato could simply dissolve the potato if stored a little on the warm side. Maybe the potatoes were somehow stored over the last few months or even the entire winter...maybe this year's hot summer is special...I'm sure that there are many other possible explanations here.

So, what is the most likely explanation?

More details:

The bananas were a ripe yellow even from purchase, and did get some brown spots of ripening, but never seemed to go through the full blackening spoiling process I am used to. The banana fruit itself behind the peel had not darkened like normal over-ripened bananas. It was standard "ripe yellow", just somehow decomposing to liquid/mush throughout the bottom half of the banana. The peels had some brown spots like normal ripening, but never developed black spots (black spots are my usual indicator that I need to eat them within a few days or the interior will start to get mushy, but these particular bananas never had this indicator).

I did not see any eyes/sprouts grow from the potatoes like I normally do (and they had no green on them, these are huge perfectly-tan russet potatoes).

For both, the unspoiled parts tasted good.

As for the kitchen temperature, it has been a bit hot (maybe as high as 80F inside) for the first few days and normal (about 72F) for the last few days. As for the kitchen humidity, it has been normal always (about 55%). The purchase and storage was in Minnesota.

If this ever happens again, I will make a video of the spoiling mush to help explain this better.

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  • 1
    How warm is it in your kitchen? Both of these prefer cool places. Potatoes also don’t like moisture. It’s also worth giving potatoes a slight squeeze and making sure they’re firm when you buy them. And bananas can turn mushy at warm temperatures even when only moderately spotted
    – Joe
    Commented Sep 10, 2023 at 0:04
  • Kitchen temperature is in the question already: It probably got as high as 80F in the afternoon the first few days, which I know is a bit warm, but other potatoes and bananas that I have purchased have not had this problem.
    – bobuhito
    Commented Sep 10, 2023 at 0:27
  • Oops, missed that. I’ve been keeping my thermostat at 80F this year, and I can confirm that bananas go from yellow to soft in just under a week. That seems fast for potatoes unless there’s already a problem with them (and I’ve bought bagged potatoes and found a bad one in there, so they might have had a head start)
    – Joe
    Commented Sep 10, 2023 at 0:53
  • Oh, but I didn’t have ‘water oozing out’. That seems past soft. Mine were still pale inside, well spotted outside. At 80F and today marks a week.
    – Joe
    Commented Sep 10, 2023 at 0:55
  • Find me a banana that lasts longer than a week, no mater what.... Potatoes shouldn't go bad in a week, unless you didn't bag them yourself. (?) pre bagged from Aldis go bad in a week; I stopped buying those. If half of them have a bad one in it, then the rest aren't far behind.
    – Mazura
    Commented Sep 10, 2023 at 20:59

2 Answers 2

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This sounds like soft rot on the potatoes. Soft rot tends to ooze "water" from the lesion and release a foul smell as it breaks down the potato. The potato will still look white and be mushy, like very loose mashed potato. This is caused by a few genera of bacteria, but commonly Pectobacterium carotovorum.

Freezing damage doesn't smell unless also infected with something, and usually is "glassy"/translucent looking rather than white.

Pectobacterium does infect bananas, but as far as I can tell, mainly manifests as infection of the plant itself, causing wilting and death of the whole plant overall, rather than just the fruit. If there was no smell from the fruit, it might not have been rotten with this genus of bacteria, though other genera are possible. "Water" leakage without the outside being blackened (if you've ever frozen a banana to store for later baking, you will know they go completely brown at the frozen area) indicates rot rather than freezing in this case too.

It is possible that one contaminated the other, but it equally likely that you have a coincidental infection of both.

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  • Thanks, I think you're right, but suspect one contaminated the other since I did have the bananas on top of the potatoes on the car ride home (or maybe ethylene gas transfer is involved?). Strangely, my banana mush halves did not have a bad smell, at least I didn't notice, though the potatoes had a terrible smell. And, strangely, my bananas did not seem to have any symptoms of rot on the stems/peels, only the mush of the fruit itself. I will mark this as the answer if nothing more logical comes within the next few days.
    – bobuhito
    Commented Sep 10, 2023 at 14:24
  • By the way, I also had red onions nearby, which I have heard also releases ethylene gas and gets everything ripening quickly. Maybe this is "the perfect storm". The onions still have no problems (like mush or general rot or bad smell), though the outer few layers by the stem are a little "rubbery" (probably normal?).
    – bobuhito
    Commented Sep 10, 2023 at 14:32
  • When you mentioned bananas and potatoes I had a funny feeling already, but I was glad you didn't mention onions because that would have completed the trifecta. But here we are! If you Google "foods you're not supposed to store together", most of the results discuss ethylene producers such as bananas, and the top result suggests keeping onions away from potatoes. Not saying any of this is obvious if you don't specifically search for it, but it does seem that you have found yourself in the unfortunate position of having happened to bring together some of the most problematic foods there are!
    – matt_rule
    Commented Sep 10, 2023 at 18:10
  • Costco does place the onions and potatoes along side each other, by the way. But, let me say again, whatever that "ethylene-multiplier" effect is, I think bacteria is also needed to cause this mush.
    – bobuhito
    Commented Sep 10, 2023 at 18:43
  • @bobuhito onions and bananas will cause the potatoes to sprout, but shouldn't cause rot. Short exposures to ethylene are fine (e.g. car trip home with them both in the same bag) - just don't store them together. Though I should add ripeness can result in faster decay from an infection. The lack of smell from the bananas indicates not the same contaminating organism, as a Pectobacterium infection generally smells quite strong.
    – bob1
    Commented Sep 10, 2023 at 21:05
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I used to buy potatoes and keep them in a plastic bag and found they would sprout and get rotten shortly after. Then my mom said keep them in a paper bag and put them in a dark place. So that’s what I did and they last much longer. They can breathe, and no moisture accumulates. Check them frequently to make sure they’re not starting to sprout or get soft. If so, then break off the sprouts and put them in a refrigerator drawer until ready to cook.

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