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My 9 year old niece asked me this when I was explaining some stuff to her about the coronavirus. She asked "What does this virus taste like? Can I tell whether my sandwich is contaminated for example?"

That sounded like a silly question and I immediately responded by saying that they are too small to have any taste, and even if you manage to eat a whole lot of viruses it would taste like water.

The day after, I searched a bit just to make sure that I haven't fed the wrong information to the kid. As I expected, there wasn't a single page mentioning this question (except this quora post with a vague answer). Now it may sound like I am overthinking and the question is too naive and isn't worth the time, but then again, I thought what's the harm in asking?

Has there been any research on the likely taste or maybe smell of a specific virus or bacteria?

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    $\begingroup$ While I don't think it's the bacteria themselves that cause the taste, there are quite a number of foods - cheese is a prime example - that acquire their taste as a result of bacterial action. And if you want to expand that a little to include microorganisms in general, there's bread, wine, beer and more. $\endgroup$ – jamesqf Jun 11 at 16:26
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    $\begingroup$ I think this is a very good question, but from the title i had assumed it would be about the sensory organs of bacteria. $\endgroup$ – Ivana Jun 12 at 12:29
  • $\begingroup$ same; too few characters for a title edit: ... have [a] taste [to them]? $\endgroup$ – dlatikay Jun 12 at 13:28
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    $\begingroup$ ... have a flavour (or "flavor" according to, er, taste) $\endgroup$ – RedGrittyBrick Jun 12 at 18:40
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    $\begingroup$ I know that mold has a taste. $\endgroup$ – Peter - Reinstate Monica Jun 14 at 13:58
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As you could imagine, a systematic cataloguing of bacterial or viral flavor profiles would violate a number of biosafety protocols. However, in a laboratory setting, different bacteria definitely have distinct odors. In some cases, the odor is even included in guidelines for laboratory identification of an organism. However, that odor is typically not a result of smelling bacteria directly, as very few bacteria are aerosolized from a lab culture. More likely, the odors of bacteria are a result of volatile chemical metabolites produced by the organisms. For example, the spoiled milk smell comes from a number of odiferous compounds produced by bacteria. Sometimes these bacterial metabolites have rather colorfully descriptive names, such as putricine or cadaverine.

Viruses are different though. They don't generate new metabolites on their own (outside of an infected cell) and they are incredibly tiny, even compared to a single cell. The human sense of taste is sensitive enough to detect some compounds in the low parts per million range. To even approach that range, you'd have to cram around 100 billion virus particles into a single milliliter of water (based on back of the envelope calculation). That's about 100,000 times more virus than most COVID19 positive clinical specimens, so I don't think you'll have to worry about tasting it under most circumstance. However, some research has been done to see if dogs can sniff out viral infections (likely by detecting volatile compounds produced by the infected cells, not by detecting the virus directly). Of course, they're trying to train them to detect the novel coronavirus as well.

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    $\begingroup$ To add another back of the envelope calculation, assuming the virus particle to have density 1 (order of magnitude) and a diameter of 80 nm (for the solid sphere), we'd expect roughly 1e-16 g per particle, so 10⁴ - 10⁷ SARS-CoV2 particles/ml should be 1 pg/ml - 1 ng/ml. Humans odor detection threshold for geosmin in water is 6 pg/ml, so in the mass concentration range of the SARS-CoV2 samples. Of course, I picked geosmin because we (those of us who do have the receptor) are extremely sensitive for geosmin. But then, that's maybe not an accident: geosmin is produced by molds, and this warns us $\endgroup$ – cbeleites unhappy with SX Jun 11 at 22:48
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    $\begingroup$ of mouldy water. (Geosmin also occurs in other mixtures such as some plants and actually in substantially higher concentration and IIRC contributes to the smell/taste - but in those combinations doesn't produce the ugly/warning sensory impression we get if it is in [more-or-less pure] water) $\endgroup$ – cbeleites unhappy with SX Jun 11 at 22:50
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    $\begingroup$ dogos? doctor doggo? :) too small for edit $\endgroup$ – dlatikay Jun 12 at 13:34
  • $\begingroup$ It's an okay generic answer, I hope it's not too critical to say it avoids the question a little and makes it about odorants; the questioner is asking about flavour (taste!). I mention it because it's unclear from your answer that taste is a different beast from smell. Certainly a little misleading to discuss concentration (parts per million) when there exist no chemoreceptors to even detect viruses or cells... There are <1 elephant parts per million in a gallon of water too, but I'd bet you wouldn't be able to taste whole elephants, regardless of how sensitive our noses and tongues would be! $\endgroup$ – S Pr Jun 15 at 7:49
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So I think this is a more conversational kind of question. I will address some misconceptions you have, and I will try to keep it brief, considering the nature and depth of your question. One could comment on the question very deeply, so I'll stick to addressing some misconceptions.

Can I tell whether my sandwich is contaminated for example?

Usually you can taste contamination because of the (action of) metabolic products of microorganisms. You do not taste nor smell the microorganism directly; you taste their metabolites or the effect of their presence, such as products of fermentation, or oxidized molecules which are normally not present because air does not penetrate through e.g. apple skins. Take filamentous fungi, for instance; they release enzymes that act on complex carbohydrates to break them down. You cannot taste the cellulose which makes up the majority of a stalk of celery, but you may be able to taste its broken down products once a fungus has begun to digest it prior to absorbing its nutrients: sweet glucose, sucrose, trioses, some acids. It depends on the food and the extent and kind of contamination.

they are too small to have any taste and, even if you manage to eat a whole lot of viruses it would taste like water.

You can taste molecules which are far smaller than a virus. Indeed, pheromones and volatile or sticky chemicals and all that jazz are definitely much smaller than viruses. Viral particles themselves may actually be too big to taste, because your sense of gustation and olfaction depends on the interaction between tastant or odorant molecules and corresponding receptors, which are situated on the membrane of sensory neurons (nerve cells which are responsible for detecting and relaying information to the brain about the outside world). These receptors harbor ligand-binding pockets that are too small to capture entire viruses. This does not rule out the ability for you to taste broken bits of viruses, but I think this is unlikely or coincidental (i.e. the particle may bind to receptors weakly and not very well).

it would taste like water

Water is a requisite for taste and smell, things have to be dissolved in water for you to be able to detect them. Water by itself has no taste! Only impurities, oxygenation and carbonation and mineral content give water flavor. I understand that you factor in temperature and texture into the 'perception of water', but these are not gustatory phenomena and use different mechanisms of detection.

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    $\begingroup$ Water is a requisite for taste and smell, things have to be dissolved in water for you to be able to detect them - Why is that so? $\endgroup$ – Rafael Eyng Jun 12 at 2:39
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    $\begingroup$ Re "things have to be dissolved in water for you to be able to detect them", is this really the case? Most tastes are the same as smell, and the odor molecules are generally not dissolved in water, unless you're including water that's present in body fluids at the odor receptor. $\endgroup$ – jamesqf Jun 12 at 4:42
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    $\begingroup$ "pheromones and volatile or sticky chemicals and all that jazz" are even on the large end of the spectrum. We can taste NaCl, and it doesn't get much smaller than that! $\endgroup$ – terdon Jun 12 at 11:11
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    $\begingroup$ Capsaicin can certainly be tasted, and that's negligibly soluble in water. It's fat-soluble though; the fat isn't even miscible with water. $\endgroup$ – Chris H Jun 12 at 11:17
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    $\begingroup$ @ChrisH It's a pretty clear cut distinction. Taste receptors are part of a well defined subset of the nervous system that processes gustatory inputs from specialized sensors. Olfactory receptors are part of a separate system that process smells with their own specialized sensors. Capsaicin triggers pain receptors, which are of a totally different sort. TRPV1 is a nociceptor that forms part of the body's thermoception system. There's no way we could consider it related to taste. $\endgroup$ – J... Jun 12 at 18:27
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Already 2 good answers (MikeyC and S PRr), but one point missing:

We are very good at detecting the presence of some bacteria and fungi in our food in unhealty amount. We detect (by smell or taste) the products of these microorganisms as "food gone bad".

That's how we survived when the food didn't have expiry term labels mandated by the government.

We are also very good at avoiding places and things that smell bad. Bad smell is an indirect indication of an unhealthy thing, probably having bad viruses and bacteria ready to get us.

Then again, most microorganisms that make us ill actually don't eat much of our food. They hide in the food (or elsewhere) in order to eat us. That's why we cannot detect most of them. They don't leave much of a chemical trace.

Viruses are even harder - they do nothing outside of the host and there is too little of them in order to sense them directly.

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    $\begingroup$ We detect (by smell or taste) the products of these microorganisms as "food gone bad". isn't that because of bacterial products instead of bacteria themselves? Since OP asked specifically about the taste of microbes, the other answers didn't talk much about their products (but still touched upon it). Not saying that your answer is bad, but it sure needs some references ;) $\endgroup$ – another 'Homo sapien' Jun 12 at 12:27
  • $\begingroup$ @another'Homosapien' a lot of taste and smell sensation comes not from the main substance or object one smells and tastes, but from the product of the object interactions with the environment and/or degradation/decomposition of the substance or object, and/or some by-product from the object/substance creation. We say "smell of rotten eggs" and not "smell of the substance that rotten eggs evaporate". $\endgroup$ – fraxinus Jun 16 at 15:01
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    $\begingroup$ Yup, I get that. But my point was that OP specifically asked about the taste of microbes, not their products (maybe I'm being pedantic here). There's nothing about your answer that is wrong or I don't understand, it's just that it doesn't answer the exact question. Also, the answer lacks the much-required references :P $\endgroup$ – another 'Homo sapien' Jun 17 at 6:52

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