I have always relied on my sense of smell to determine whether meat (most often chicken) is bad and I thought it was reliable. However, I have just heard that [1] smell is not always reliable, since some of the toxins produced by bacteria won't cause any smell whatsoever and you won't be able to notice that the meat is off until after you've eaten it.

Is this true? If yes, is this true for all meat or only for some? Is there a more reliable way of determining whether meat is still good.

[1] "Heard that" isn't very reliable; so that's why I'm asking the question here. :)

2 Answers 2


It is absolutely untrue and very dangerous to think that "if it looks OK, and smells OK, it must be OK." If that were the case, food poisoning would be very rare.

Food that we can sense is spoiled rarely causes illness. For one thing what you don't eat can't hurt you, and people generally won't eat food that looks or smells spoiled. But less obviously, much of what causes spoilage that we can taste, see or smell is actually fairly harmless to humans. Spoilage and rancidity are terms that are often used interchangeably, but rancidity is actually a specific kind of spoilage, caused by the relatively harmless oxidation of fats which is unrelated to any kind of bacteria or other microorganism. It's just a function of time, temperature, oxygen, and light. Fancy dried cured meats get a fair amount of their special flavor from controlled rancidity. Molds and yeasts cause food to spoil, but are also used in controlled ways to create flavor. Dairy cultures are bacteria, and bacteria plays a major role in fermentation.

What causes illness and death are usually things that we can't taste, see, or smell. Salmonella, E. coli and C. botulinum are often undetectable by our senses. Mishandled food that has been heated to temperatures far hotter than is necessary to kill any and all dangerous organisms can still kill if those organisms have produced chemical toxins or deadly spores. We often can't sense those either.

That's why the rules exist. It is critically important to take care to keep food out of the dreaded "danger zone". Foods that are considered unsafe unless cooked to a specific temperature ARE unsafe unless cooked to that temperature (although government recommendations in that matter are often overly conservative, there is room there for assessing your own risk). Preserved foods must have appropriate acid, salinity, sugar or other tested preservatives. Stored foods must be kept at the proper temperature. Dried foods must be dried correctly. Canning procedures rules seem overly strict. They are not. Learn the rules, disobey them at your peril.

There is a lot of good information here under the tag. We are not making this stuff up. The CDC "estimates that each year roughly 1 in 6 Americans (or 48 million people) get sick, 128,000 are hospitalized, and 3,000 die of foodborne diseases." That's just in the US where food handlers (home and professional) are mostly educated in basic food hygiene and just about everyone has access to a refrigerator. The worldwide figures are staggering.

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    But those pathogens would be killed by cooking, so that's not the problem. The problem that I was talking about is toxins produced by the bacteria that won't be destroyed by cooking. Most of the toxins I was aware of give off a clear smell, but 'apparently', there are also toxins (in meat) that don't do that.
    – Ben
    Jun 22, 2014 at 12:46
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    @Ben: Bacteria are killed by cooking, but the cooking temperatures provided by food safety agencies are specifically designed for typical levels of contamination found at the supermarket and so on - not for petri dishes containing billions of times more bacteria than normal. It's true that toxins are the more serious issue because they can't be killed, but even with the bacteria, it's not a "yes" or "no" question, it's a "how many" question; even if there were no toxins, you might have to considerably raise the cooking time and temperature to kill the additional bacteria.
    – Aaronut
    Jun 22, 2014 at 13:03
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    @Aaronut Actually, some toxins can be "killed" by heating. The biological effect of proteins depends very heavily on their shape, which destroyed by suffient heating. This process is exactly what causes egg white to change from a slimy, almost colourless liquid to an opaque white solid when fried; in fact, it's why heating kills the bacteria that made the toxin, too. The botulinum toxin is a protein that denatures at 80C but please do not assume that you're safe from botulism if you heat something to 80C. Jun 22, 2014 at 17:20
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    @DavidRicherby: You're covering subjects that have been extensively discussed on this site. Toxins can't be killed because they aren't alive. They can be denatured, but for many toxins the denaturation temperature is so high that your food would be charcoal if you reached it. Thus we simply consider sufficient bacterial contamination to be an unrecoverable situation and tell people "when in doubt, throw it out".
    – Aaronut
    Jun 22, 2014 at 17:31
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    @Aaronut That's why I put the word killed in inverted commas. Jun 22, 2014 at 17:41

Basically there is no right or wrong advice here, mainly because most people don't know, and have never learned to trust their senses. Long story short: After cooking or flavoring there is no halfway reliable way determining 'rotten' foodstuff.

Long story long: We're the product of billions of years of evolution. Two centuries ago nobody knew about bacteria, microbes, their toxins and what really happens when food gets spoiled, no freshness dates and so on. But we wouldn't have lasted a decade without sensing spoiled food before eating a stack of rotten meat. So YES, we CAN detect rotten foodstuff. It's just not easy, involves quite a bit of trial and error, and overall depends on your cleverness not to eat something that tastes bad.

Let me give you an example: The botulinum toxin is produced by different specimen of clostridium botulinum. It is one of the most toxic substances mother nature is able to throw at us, and it's undetectable by any sense (unless it's too late). BUT: One must be a quite stupid fellow to get lethally intoxicated (by spoiled food, that is - not counting the Botox faces). So why is it that hard to die of this poison? Clostridium is a bacteria that loves meat (as almost all microorganisms do), but it hates oxygen. It won't grow colonies on the finest meat if exposed to air. To maintain the metabolism it can't just produce the quite complicated toxin, it has to digest something, like proteins, fat or sugar. During this digestion it produces massive amounts of substances we can detect, like butyric acid, acetic acid, acetone and other fine stuff nobody sane would eat. In fact most people will instantly feel a strong urge to gag or even puke if presented with the acid-sweet smell of botox meat in the morning. [ed. Please refer to the comments. I suggest the struck-out text is dangerous if understood to be the whole truth.]

The same is with almost all other food poisoning stuff - if your fish smells like it has had a quite long sunbath, it most probably isn't save to eat any longer. If your chicken feels like somebody oiled it with egg white, it has had some quite similar treatment by some small guys you dead sure don't like to eat.

So eat and drink as you fancy, but don't eat stuff that tastes awkward (and isn't supposed to do so - some people like funny tastes, and some tastes you have to get used to). Of course it will lead to wasting some food that still is good and proper, but it keeps you safe for a quite long time. It worked the last few billion years for a massive amount of species, why should it stop working now?

And, as others pointed out before: Microbes are no problem. LOADS of the wrong type present one. Some people can eat quite rotten stuff without any problems, for 1st-world citizens this won't work that good. You have to get used to the microbes you eat, and you will get a higher tolerance threshold for most toxins and microbes when eating/drinking mostly 'infected' foodstuff. That's why the average Indian can eat the ice cream on the market by the ton, while it will give you quite some friendship time with Mr. Toilette if just eating a small one.

By the way: Always being on the safe side is not that good either, because if you find yourself in front of the wrong plate one day, you will have the time of your life. Or not. Our immune system (and everything connected to it, like your gastro-intestinal system) is like a muscle - if you don't train it, it will always be weak and thus break down on every occasion. And most food poisoning problems (like salmonella) are breakdowns of your immune system and/or your gastro-intestinal flora.

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    @Jolenealaska's statistics on foodborne illnesses entirely undercut your point here. Yes, natural selection has given us some instincts that help identify spoilage, but these are heuristics and prone to potentially dangerous errors. They should not be relied upon, especially not when preparing food for others. This advice strikes me as questionable at best, and irresponsible at worst.
    – logophobe
    Jun 23, 2014 at 15:18
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    I would argue against most of your points because obviously we can't reliably sense if food is dangerous, because if we could, we simply wouldn't eat that food. One point that you bring up is valid. I call it "bubble-boy syndrome". I have eaten meat very, very rare my whole life. I've never been sick from it and I doubt I ever will. I'm sure I have strong and healthy e-coli busters. That's a similar phenomenon to your example of an American eating ice cream in India. I don't think we do ourselves any favors by trying to maintain sterility in the kitchen.
    – Jolenealaska
    Jun 23, 2014 at 16:43
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    "[...] most people will instantly feel a strong urge to gag or even puke if presented with the acid-sweet smell of botox meat" Correct me if I'm wrong, but I believe this is only true for proteolytic strains, in which case group II strains of C. botulinum, being non-proteolytic, will produce neurotoxins without any strong odor. Jun 23, 2014 at 18:26
  • @logophobe Believing the statistics of the RKI for 2011 and 2012 there were 9/0 incidents (2011/2012) for Botulism in Germany, 71k/62k for Campylobacter, 4/0 for Cholera, 8k/7k E. coli, 5k/1.5k EHEC, 880/69 HUS, 644/655 Legionella, 116k/113k Norovirus, 54k/39k Rotavirus and 25k/21k Salmonella, so roundabout 280k/244k incidents of potentially food related intoxications for 87M Germans who eat about 3 meals a day for 365 days a year. Given all incidents were food related (and about half were prepared by ordinary people) only 2.5 meals per million were contaminated. I'd say my point is valid. Jun 24, 2014 at 15:46
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    @Metal_Warrior That might be an argument for your point if the only food safety standard being followed in Germany is "if it smells bad, don't eat it". But it is not. If anything, that's an argument for the effectiveness of modern food safety standards. It says nothing whatsoever about whether the "sensory" method of detecting spoilage is reliable. And I would continue to assert that such a method is most definitely less reliable than using government-issued safety guidelines.
    – logophobe
    Jun 24, 2014 at 16:34

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