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I've been encountering a perplexing issue with my mashed potatoes, and I'm seeking advice from the experienced cooking community. After boiling and mashing the potatoes, they seem to spoil remarkably quickly, often within just two hours of preparation. Here's a breakdown of my usual process:

I boil the potatoes (with the skin on) in a pressure cooker for three whistles. After boiling, I let them cool slightly (like maybe 10 mins) and then peel and mash them while they're still somewhat hot, as I find it easier to mash them at this stage.

The problem is that within 2 hours they start becoming very sticky. If you pick up a lump and try to break it apart with your fingers you can see the sticky lines popping out between them. So they're definitely ruined.

I don't think I'm doing anything wrong in my cooking method. I don't see any reason that could lead to rapid spoilage. But if I keep them out for 2 hours I can see that they become somewhat sticky (as you can make out if you tear apart a piece with your fingers.

I'd like to understand why this might be happening and how I can prevent it. Has anyone faced this before and overcome it?

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    What are you adding to them?
    – Stephie
    Commented Oct 14, 2023 at 11:44
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    What makes you think they’re “spoiled”?
    – Sneftel
    Commented Oct 14, 2023 at 11:58
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    How long is "three whistles"? As someone who's never owned a pressure cooker, that means nothing to me. I also can't really figure out why you'd a) boil potatoes with the skin on then peel with the extra waiting time & mess of trying to peel something soft, or b) why you'd need a pressure cooker for something that only needs boiling for 10 minutes anyway. It gives me the impression you're probably over-cooking them.
    – Tetsujin
    Commented Oct 14, 2023 at 13:16
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    So, next time peel them first, so you can mash them straight away. You'll also have a better test for 'doneness' - if they're underdone a fork won't split them, if they're over they'll start to collapse into the water. That will let you adjust your timings for next time.
    – Tetsujin
    Commented Oct 15, 2023 at 11:15
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    I'm confused why you're using a pressure cooker, which is generally used to speed up long slow processes, on a really short process, and then leaving the cooked product unused for hours. Why not boil the potatoes closer to the time you want them? Commented Oct 16, 2023 at 12:57

2 Answers 2

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What you are describing isn't spoiling, what you are describing is not the product of bacterial growth that would cause food to go bad. If it had gone bad you'd have nasty smells and flavors, you are having an issue with consistency, not spoilage.

The most likely cause of your problem is that you are overcooking the potatoes. Overcooking will cause the potatoes to break down too much, giving you a gluey texture which you will notice more when your mashed potatoes are cooler.

I'm not a fan of cooking potatoes in a pressure cooker because you can't check them as you cook. For mashed potatoes you want them to be done enough to easily split apart when you stick a fork in, but where you still need to work at it a bit to mash them. Reduce the cooking time, and if you want to use a pressure cooker use a timer rather than whistles, as the time between whistles varies by brand and other conditions. Or, use a regular pan with lid to cook them.

Other suggestions I have would be to peel the potatoes before you cook them, and to cut them into smaller pieces. With large chunks the outside will overcook and dissolve before the inside is done, smaller chunks will cook more evenly and give you a more consistent result.

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  • I prefer cutting slabs to dicing it… you have more consistent cooking times (no corners and such), with less work. There are also some recommendations out there to simmer the potatoes for a while instead of boiling, as supposedly that changes the starch to keep it from becoming gluey.
    – Joe
    Commented Oct 16, 2023 at 13:09
  • I'm going to try slabs next time @Joe. Mashed sounds good right about now.
    – GdD
    Commented Oct 16, 2023 at 18:01
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    “If it had gone bad you'd have nasty smells and flavors” — not necessarily.  Some microbes can produce nasty smells/flavours/colours, but others are undetectable (without biochemical equipment — or by the effect it might have on you…)  So taste and appearance are not necessarily an indication of safety; that's why we have guidelines such as in Ecnerwal's answer.
    – gidds
    Commented Oct 17, 2023 at 13:32
  • I would not expect 2 hours to be long enough for the food to spoil, in any case my point is that the issues with the mashed potatoes' consistency is not due to bacterial growth.
    – GdD
    Commented Oct 17, 2023 at 13:51
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    It's not spoiling @Mugen, that's the wrong term. Spoiling implies food safety concerns where this is a problem with texture. Although I have overboiled potatoes in the past it's a mistake I only made once, so I haven't observed how quickly the texture turns to goo.
    – GdD
    Commented Oct 17, 2023 at 16:50
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If you "keep them out" (presumably meaning unheated and unrefrigerated) they are halfway to throwing out at 2 hours from a food safety point of view (where the common metric is that they should be disposed of after 4 hours in the bacterial danger zone temperature range between 140°F/60°C and 41°F/5°C.) I have no idea why you'd prepare them and then hold them for two hours, but if you are not going to eat them when prepared they either need to be held hot or rapidly cooled and refrigerated.

"Become somewhat sticky" is not a sign of spoilage (in the food safety sense,) it's probably the starch gelatinizing. Unappealing as mashed potatoes, but not a clear sign that it will make you sick if you ate it. But better to make the potatoes closer to the time they will be eaten so that they are more appealing.

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  • I did not know that it's not common to keep them out for a few hours. So what you're saying is that after boiling the potatoes we should not peel them (if we're not going to use them immediately). Is that correct? And any idea how long we should keep them out (unpeeled) before we can keep them in the fridge without causing any spoilage?
    – Mugen
    Commented Oct 15, 2023 at 11:09
  • When I say "somewhat sticky" - if you pick up a lump and try to break it apart with your fingers you can see the sticky lines popping out between them. AFAIK, that is spoiled.
    – Mugen
    Commented Oct 15, 2023 at 11:10
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    @Mugen What you're describing isn't spoilage, it's the development of the starch from the potatoes. Boiling starchy foods causes starch granules to rupture, allowing the starch to spread through the liquid. As the liquid cools, the starch molecules begin connecting with each other and produce a sticky, glutinous material. It's not harmful to eat, and in fact such gels are the basis for many foods, such as puddings.
    – barbecue
    Commented Oct 15, 2023 at 23:44
  • @barbecue A massive portion of Italian pasta dishes in particular would not be possible without the gelatinization of starches.
    – Abion47
    Commented Oct 16, 2023 at 17:40
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    @Mugen Yes, I'm very sure. Potato starch is actually used to make glue because it produces such a sticky gel. intercol.info/adhesives/hot-melt-en-lijm/…
    – barbecue
    Commented Oct 17, 2023 at 18:42

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