Stupid question [?]: why does rotten food stink?

Boy, this really seems like a stupid question, right? Of course it does. Take fish. A few days old, and you can't get the stink off of you. All of us test for freshness by smelling the fish and looking for bright eyes. If they pass the smell and bright eye test, we'll buy them and cook them up as soon as possible.

It's obvious, right? They are old and they stink.

But maybe not.

Maybe microbes find the dead fish and make them smell bad, so that other microbes and animals and folks like me won't eat them. Leaving the fish for the microbes that produce the bad smells to feast and reproduce and spoil lots of other stuff.

Might be. Take a look at

http://www.physorg.com/news81603081.html

[NPR had a short essay on the topic today as well:

http://www.npr.org/templates/story/stor ... d=14447250 ]

Maybe if we can prevent the microbes from creating that horrible smell, we can prevent food from "spoiling" -- some folks estimate that a third of all food spoils before humans can eat it.

Maybe not such a "stupid question" after all.

Regards, Bob

The scientist in the NPR bit suggests it isn't so, but my sense is that natural selection has taught us to recognize what is good to eat and what isn't oftentimes by the smell. The microbes appear to be just taking advantage of this, i.e. microbes which can produce the stench are adapted and have survived because of it. They fake us out.

As a footnote, we seem, however, capable of overcoming the repulsion, e.g. stinky cheeses and maybe a really barnyardy pinot noir.

Interestingly enough, before my body starting objecting to seafood, I never had a problem with fish aromas. They were at times mouth-watering. Now that certain seafood really challenges my system, even fresh fish smells repulsive to me. That is probably a learned defensive behavior, but seems to illustrate the argument for naturally selective processes being at work.

Does rotten food smell? I never noticed...

I think it's more the other way around. The microbes responsible for food spoilage produce substances that are toxic to humans. Natural selection has left our sense of smell extremely sensitive to substances that these microbes emit, even if they occur in very tiny concentrations (parts per trillion, in some cases). Our instinctive aversion to even the slightest whiff of these substances prevents us from ingesting food contaminated with dangerous live microbes, or their toxins.

I think it would be a very bad idea to suppress the generation of these spoilage odors. It would leave us with no warning concerning the other (and dangerous!) things present due to the microbes in the bad food!

-Paul W.

But, Paul, I think the idea is to prevent the microbes from being in the food, or at least to slow down their growth.

Of course, without more research, we don't know if the microbes are dangerous at all, and are just staking out a prior claim.

Stuart, where are you? We need you over here.

rwj

But, Paul, I think the idea is to prevent the microbes from being in the food, or at least to slow down their growth.

Of course, without more research, we don't know if the microbes are dangerous at all, and are just staking out a prior claim.

The microbes that produce putreicin and related stinky compounds might be harmless, but their presence indicates that the food (which after cooking is more or less sterile) has been colonized by microorganisms from the ambient environment. There may be lots of other things growing in there that are NOT harmless, but the stench from the harmless ones indicates their possible presence.

-Paul W.

But wouldn't cooking solve that problem, Paul?

I'm sure there are many microbes from the ambient environment in even fresh food, let alone aged beef or fowl or even my beloved Lutefisk , for example.

I suppose sushi might present an additional challenge to be sure it was really fresh fresh, but that wouldn't be a reason to avoid a technology designed to save food.

But wouldn't cooking solve that problem, Paul?

I'm sure there are many microbes from the ambient environment in even fresh food, let alone aged beef or fowl or even my beloved Lutefisk , for example.

I suppose sushi might present an additional challenge to be sure it was really fresh fresh, but that wouldn't be a reason to avoid a technology designed to save food.

You just said "food" in your original post. I thought you were talking about spoilage in cooked/prepared food as well as in fresh ingredients.

Cured ham, aged beef/fowl, yogurt, ripened cheese, etc., are cases of carefully controlled bacterial culture, even when started from ambient microbes. Again, the presence of off-odors in these processes is an indicator that you are culturing things beyond the bugs you intend to culture. They are the only warning sign that something has gone wrong. I think it would be highly dangerous to eliminate that.

-Paul W.

I don't know why rotten food stinks..

All I know is that I thought I was going to have to throw out my daughter's lunch box. I was gone for 5 days. Her lunch--a salad with pieces of roast chicken and a touch of caesar dressing--was NOT gone for 5 days. It was, in fact, very much at home in said lunch box.

Rotting.

Decay. Death. Vomit. Gross..

Bleach. Simple Green. Febreeze. Dish washer. Bleach again.

I think it may pass the sniff test. but if not, there goes the brand new box into the trash

All I know is that I thought I was going to have to throw out my daughter's lunch box. I was gone for 5 days.

Isn't it good to know that you are needed?

Cooking does not solve the problem of microbial contamination in all cases. Many microbes produce toxins, e.g. botulism, that survive cooking.

Paul has it right. Evolution has selected for sensitivity to odors that correlate to spoilage. Note that correlation is the key. Not every spoiled foodstuff is dangerous to eat. We learn to identify forms of spoilage that are safe to eat - like stinky cheese, fermented fish (e.g. nam pla and anchovy paste), durian.

The microbes that cause rot-induced putricene might not be the dangerous microbes. They might just indicate that other dangerous microbes, like salmonella, are present. Salmonella is not odorous and cannot be detected by our senses, so we have adapted to this kind of health threat by heightening our sensitivity to other effects that correlate highly with the ones that are dangerous.

But other animals, like scavengers, have immune systems that have adapted to the microbes and toxins that are dangerous to us. Vultures, for example, are attracted to putricene!

But rotten food doesn't hurt vultures, Bernard. Humans are one of the broadest range omnivores that exist -- we seem to be able to eat anything, really.

Unless we create a barrier in our minds, of course.

Whatever we discuss here, the observation is really interesting, and worth exploring further.

Regards, Bob

But rotten food doesn't hurt vultures, Bernard. Humans are one of the broadest range omnivores that exist -- we seem to be able to eat anything, really.

Regards, Bob

I don't understand your point, Bob. Perhaps you didn't understand mine.

I may not have understood your point, Bernard. As far as I know, there is no correlation between Salmonella, for example, and microorganisms that cause food to stink. The CDC entry on Salmonella reads:

Salmonella live in the intestinal tracts of humans and other animals, including birds. Salmonella are usually transmitted to humans by eating foods contaminated with animal feces. Contaminated foods usually look and smell normal. Contaminated foods are often of animal origin, such as beef, poultry, milk, or eggs, but all foods, including vegetables may become contaminated. Many raw foods of animal origin are frequently contaminated, but fortunately, thorough cooking kills Salmonella. Food may also become contaminated by the unwashed hands of an infected food handler, who forgot to wash his or her hands with soap after using the bathroom.

My understanding of the research I quoted above is that the microorganisms in question are making the food unattractive to other organisms, to benefit themselves. They don't seem to be dangerous themselves.

There may be a symbiotic relationship between the stink producers and other, more dangerous, organisms, but it would seem to be worthy of further study to find out. And, if there is such a relationship, perhaps by killing the stink producers, the other organisms might not be able to develop.

My observation wasn't about salmonella. I only used it as an example of a dangerous bacterium that cannot be detected by our senses because it does not cause food decay. There are, no doubt, other bacteria that are dangerous and that cannot be detected by our senses. Perhaps there is a correlation between their presence and the bacteria that cause food to decay, possibly even a symbiotic relationship.

My understanding of the research I quoted above is that the microorganisms in question are making the food unattractive to other organisms, to benefit themselves. They don't seem to be dangerous themselves.

There may be a symbiotic relationship between the stink producers and other, more dangerous, organisms, but it would seem to be worthy of further study to find out. And, if there is such a relationship, perhaps by killing the stink producers, the other organisms might not be able to develop.

I don't think it's a matter of any symbiotic relationship.

Just that if the condition of the food is such that the stinky bacteria have taken up residence, then it's possible, if not likely, that the dangerous bacteria have likely had their chance to set up shop.

I think it is this premise that has led to our own evolutionary and instinctive revulsion towards the aromatic products of the (otherwise harmless) stinky bacteria.

This is why I think any attempt to get rid of the stinky bacteria, or breed the stink out of them, is misguided. These organisms are valuable to us as the alarm bells that the food has been contaminated--by gods what knows what else that might be dangerous. They are the canaries of the food poisoning world.

-Paul W.