Who, if anyone, can smell salt water and sugar water?

August 19, 2014 8:13 PM

Can anyone smell the difference between a cup of normal water, a cup of salt water (not ocean water, just salt dissolved in water), and a cup of sugar water? And if so, who/what level of smeller, precisely? Does your answer change if the water is warm but not steaming? What about steaming?

I'm anosmic (no sense of smell) and was born that way. I have asked this question of a small group and it has been causing debate, an admittedly small and poorly executed experiment was inconclusive and probably biased, and so we now would like a large and impartial group verdict to settle the issue.

Ideally looking more for people to actually test it out, find research/data, etc. Speculation is already rampant.

posted by vegartanipla to Science & Nature (26 answers total)

I can smell the difference between the Pacific and Atlantic oceans. The Atlantic's saltier. Don't know if I can smell sugar if it's straight cold sugar water but I can definitely smell it in tea and coffee from a ways away.
posted by fshgrl at 8:20 PM on August 19, 2014 [3 favorites]

When I make brine for turkey, I can certainly smell the difference between plain water, salt water, sugar water, and salt/sugar brine.

I'd say my sense of smell is usually pretty good.

Hot liquids are easier to smell, but cold brine smells too.
posted by tomierna at 8:39 PM on August 19, 2014

My answer is pretty much the same as tomierna's. Sure, I can absolutely smell the difference between plain, salt, and sugar water (whether lukewarm, hot, cold, or steaming) and have many occasions to do so while preparing food.

I would consider my sense of smell quite good, but not unusually so.
posted by desuetude at 9:13 PM on August 19, 2014

OK, I just dissolved a tablespoon of sugar and tablespoon of salt into two small cups of water (~7 ounces each). The sugar water didn't smell sweet, exactly, but it smelled noticeably more neutral than straight tap water. The salt water smelled like salt water. I tasted both and the sugar water was sweet but not overpoweringly so, the salt water was undrinkable.

I think I have an average to fairly good sense of smell.
posted by MadamM at 9:28 PM on August 19, 2014 [1 favorite]

I just did an experiment on the sugar front. (For what it's worth, I thought that I would absolutely be able to tell the difference.)

I added two metric teaspoons of white cane sugar to a glass, added 50ml of boiling water to dissolve as much as possible, then topped up to 250ml with cold water (about 4 oC, if it's the same temp as the fridge). In two identical glasses, I mixed 50ml of boiling water and 200ml of cold water.

I left the kitchen after asking a colleague to move them around, take note of which one contained the sugar, then to leave the kitchen.

I re-entered the kitchen and tried to identify the sugar water by smell. I didn't blindfold myself, but I tried to stare straight ahead as much as possible in case there were undissolved crystals.

I couldn't tell the difference. I guessed. I was wrong.

I tasted the sugar water, and it was obviously sweet.

I will now try this with co-workers.
posted by obiwanwasabi at 9:37 PM on August 19, 2014 [11 favorites]

Iodized or non-iodized salt? That might make a difference.
posted by elsietheeel at 9:46 PM on August 19, 2014 [1 favorite]

OK:

Arranged the three samples. Asked a co-worker (who had no idea what I was doing) to come in. I said:

"Please smell each of the glasses, then tell me what you think."

Answer: "They smell like water."

"Did you notice anything about them?"

"No."

"Did one of them smell different?"

(re-smelling)

"No."

"Taste this glass."

"It's very sweet."

"Taste the others."

"They taste like water."
posted by obiwanwasabi at 9:52 PM on August 19, 2014 [7 favorites]

How much salt/sugar are you talking about? 1 tsp in a cup of water? A tablespoon? I would like to do an experiment, but I need parameters.

For what it's worth, I'm sure I can smell very salty hot water. I am pretty sure I can't smell the difference between plain water and water with sugar in it, whether hot or cold. I'm not sure whether I can smell salt water if only a small amount of salt is dissolved in it.
posted by lollusc at 9:55 PM on August 19, 2014

Response by poster: The salt is supposed to be pure salt so I guess non-iodized salt.

lollusc, the debate is multi-faceted and there is a faction claiming even a large amount of salt/sugar isn't smell-able (one member claiming the crystalline structure even when dissolved makes them un-smellable) so whether the quantity matters is also up in the air. When I asked the question, I hadn't thought it through enormously but I guess I was thinking enough salt/sugar that one could taste the difference but not like ridiculously saturated.

Other scents have been charged with "suggesting" or "carrying" the sugar/salt scent.* So the specific experiment isn't about sweet coffee or the ocean or whatnot, just water. Though I have about forty follow-up questions that this question is unexpectedly bringing up. But first we have to settle this question.

*I apologize for all the awful descriptions I'm giving - it's hard since I've only an academic semi-understanding of this sense.
posted by vegartanipla at 10:28 PM on August 19, 2014

Years ago I had a teacher make this claim so I did a crude version of the experiment at home and found the smells easy to distinguish. But I would not be surprised if changing the temperature or concentration meant it was impossible to tell them apart, or even just a more careful experimental method.
posted by Dip Flash at 10:44 PM on August 19, 2014 [1 favorite]

I can smell different types of salt, and I'm pretty side it's the minerals. Brown sugar smells different from white sugar too. Heated things have stronger smells because the aromatic chemicals are moving more rapidly to the receptors in your nose, I think.
posted by viggorlijah at 10:44 PM on August 19, 2014 [1 favorite]

Response by poster: Not to derail my own question, but viggorlijah, when you say you can smell different types of salt and sugar, do you mean in their solid state just sitting still not being stirred up? In a normal, air conditioned room that isn't really humid? Because I've been pretty consistently told no one can smell the difference between solid sugar and salt, as opposed to the confusion this question engendered.
posted by vegartanipla at 11:01 PM on August 19, 2014

Both. We keep salt and sugar in big glass jars on our countertops, and I sniff before spooning it into my cup. Sugar has a slight scent that's thin and high, salt has more of an absence of scent, a flat heaviness. I just spooned a tablespoon of plain sugar and salt into bowls and sniff tested them as powders (note I live in humid Singapore) and the sugar could be smelt, but the salt was easier to smell with a tablespoon of warm water added so it dissolved. My son who can also tell the difference between Pepsi and Coke was able to smell the difference once they were dissolved, but not before.
posted by viggorlijah at 11:17 PM on August 19, 2014

Obiwanwasabi's results are what I would have predicted. When you smell water you're breathing in water vapour; when water vaporises it leaves the salt (or the sugar?) behind, doesn't it?
posted by Segundus at 11:22 PM on August 19, 2014 [1 favorite]

Darren Logan says no.
posted by Segundus at 11:25 PM on August 19, 2014 [1 favorite]

Best answer: What you're smelling are impurities in the substances. 100% pure NaCl has no scent; 100% pure sucrose has no smell. But granulated sugar is 99.9% pure, and the longer it sits around (particularly in hot and/or humid climates) the more it slowly degrades into caramelization compounds and other aromatic compounds, which do have smells. Similarly, salt can have smells due to its impurities, the same way it can have colors.
posted by WasabiFlux at 12:13 AM on August 20, 2014 [16 favorites]

I was going to say what WasabiFlux mentioned. The outcome of the experiment will be determined solely by external circumstances. Also as an aside, I can't find the specific study, but when people were asked what special abilities they have, almost all of them listed good sense of smell, regardless of how good it actually is. We tend to overestimate our sense of smell, it seems.
posted by snufkin5 at 4:01 AM on August 20, 2014 [3 favorites]

Just tried this with me and my partner, as controlled as I could make it - single blind, three samples each of two concentrations of sugar, sea salt, regular ionized salt, plain water, didn't look at the vessels, etc. High concentration was a tablespoon in 250 mL water, low concentration was (I think, I forgot to document this) 3/4 tsp in 250 mL. New bags of regular kitchen ingredients.

I have a fairly poor sense of smell. I could accurately identify the presence of sea salt at both high and low concentration, while still steaming hot and after cooling to room temperature. I could not differentiate between the two concentrations. I could detect sugar only at high concentration while steaming. I could not smell the plain salt at any concentration or temperature. I misidentified two of the control samples as containing sugar.

My partner states he has an above average sense of smell. He could identify presence and concentration of sea salt at both concentrations at both temperatures. He could identify the presence of plain salt and sugar at high concentration and high temperature, but not the concentration. He did not misidentify any of the plain water samples.
posted by skyl1n3 at 6:56 AM on August 20, 2014 [6 favorites]

WasabiFlux' explanation fits with the non-blinded experiment I just did: putting salt and sugar onto separate paper towels and smelling them. My salt is from a sea salt shaker I recently bought, and I couldn't smell a thing; the sugar is from a bag I brought in for my tea last year and forgot about, and it smells faintly vanilla-y, which would fit with caramelizing over time.
posted by telophase at 9:42 AM on August 20, 2014 [1 favorite]

The vapor pressure of solids (i.e., their volatility, or tendency to become potentially odorous gases) is generally very low. Starting from 1 atm at the boiling point of the liquid phase, vapor pressure decreases extremely rapidly with decreasing temperature. (The relationship is proportional to exp(-1/T), where T is the absolute temperature in kelvins; here is the data for metals, some of which are more volatile than ionic and strongly bonded salt) Here is some data on the vapor pressure of salt that shows the rapid decrease; I estimate that the vapor pressure is far less than 10^-30 atmospheres at room temperature (300K), which is a totally negligible value.

You cannot smell pure salt, either as a solid or dissolved in water.

Put roughly, to have a chance of smelling a solid, it's got to disappear into the atmosphere at an appreciable rate. Pure salt doesn't qualify.
posted by Mapes at 9:46 AM on August 20, 2014 [1 favorite]

The sugar water didn't smell sweet, exactly, but it smelled noticeably more neutral than straight tap water.

Adding a solute also lowers the vapor pressure of the mixture compared to the pure solvent, so this may be the impurity argument in the other direction - maybe you're smelling the tap water's impurities less.
posted by solotoro at 2:12 PM on August 20, 2014 [1 favorite]

ok so from someone who works with chemists and labs and pharmaceutical products all day, if you want a definitive answer, you should more closely determine and define what you're trying to do here, and come up with a proper assay. Otherwise believe me you can drunkenly argue with your mates all day and never really come to any sort of definitive agreement because there are WAY too many random variables at play here. Define "saltwater". What kind of sugar are you using? How much? Are you using tapwater full of rust/chlorine/sulfur/calcium chloride (all of which have strong, characteristic odors)? And so on.

Sea salt is very different from pure salt which is very different from iodized salt, and I can tell you right now that the various sugars are ALL over the map depending on quality and brand and type and how much molasses content is in them and what lovely industrial solvents are being used in the isolation steps, and even what packaging materials are used for them. I can certainly smell the difference between various types of salt and sugar in the containers, but is it the actual compound itself or is it a side effect of the manufacturing process? As an aside, I have a pretty sensitive nose and have been used on various sampling projects in biotech and food-grade nutritional stuff over the years because of this.

Mapes is also absolutely correct that pure sodium chloride has no scent. The NaCL we use here in the labs for things like reference sampling has no odor; cooking and grocery store salts, very not so much. The French grey sea salt I use for cooking has a definite characteristic "briny" marine quality to it that I can clearly smell in solution, and frequently even in things like soups when it's dissolving.

So, pretty much you should define what you're doing here as a simple assay. If you want your assay to have demonstrable, repeatable, accurate results, you need to first specify what you're looking at, and you should use consistent methods. That means you need to do the following:

1) you need to determine a specification for your process, meaning, you need to define each solution as a specific chemical mixture of components by weight - the lab nerd term for this is "w/w" or "percent by weight". The quick and dirty way of doing this is measuring out and adding 10/20/30 grams of salt or sugar 100 milliters of water for a 10/20/30% solution - this makes it dead easy to control your solution concentrations. If you can borrow a (clean) gram scale and graduated cylinder from your friendly local OChem student, you're all set.

You also need to define the brand / type of salt and sugar that you're using in each step of your assay. You need to differentiate between using tap water and pure because impurities and chemicals in tap introduce all kinds of aromas - hot OR cold. Different types or even different batches of sugar or salt from the same manufacturer can introduce variances. So be specific. Are you sampling sea salt? Pure lab quality NaCL? Morton's table salt? Iodized or pure? Even grocery store non-iodized salt has a rather strongly characteristic smell (to me at least) of the packaging it's sold in. Are you using tap water or bottled water or distilled? Be specific in what you're defining here and you'll get more rational results.

2) you need a method that clearly outlines the parameters of your process; the exact volume of your solvent (water), the exact temperature of your solvent, and the exact concentration of your solution, meaning you must set a predetermined exact weight of sugar or salt to add to your predetermined volume of water. To do an assay you can run a matrix of varying concentrations and record the outcomes. I would suggest if you want a truly agnostic assay that you buy a jug of distilled water to run this to avoid introducing "noise" (variability) from your solvent.

So a simple assay would look kind of like this:

Specification: 10% sugar solution (room temp)

Method: Measure 10g Domino brand white sugar into 100ml distilled water in a non-reactive glass vessel at 20°C. Stir well ensuring all crystals are thoroughly dissolved into solution.

Specification: 20% salt solution (room temp)

Method: Measure 20g Morton plain table salt (non-iodized) into 100ml distilled water in a non-reactive glass vessel at 20°C. Stir well, ensuring all crystals are thoroughly dissolved into solution.

You can define your specs as whatever concentrations (w/w) sugar or salt you like, but I would stick to comparing like to like; so 10% sugar to 10% salt, using the same temperature, and so on.

To further refine your test protocol, I would blind your subjects by mixing the solutions to specification by yourself and labeling them out of their sight. Label the samples on the bottom with stickers that don't show through / can't be seen by your testers (use a clean opaque mug). Post-It notes might work well for this. Allow your subjects to smell the samples from above but not touch them or lift the sampling vessel. Record the results, and I can assure you you'll come up with a much more accurate answer to your question than a random, non-blinded array of uncontrolled anecdotal evidence on the internet :)

Scientific method. Use it.
posted by lonefrontranger at 5:39 PM on August 20, 2014 [5 favorites]

Response by poster: When I asked the question I had figured that the evaporating water would carry the scent, kind of like perfume,* and that steam would do so even more strongly. I thought it was just the solid nature of the ingredients in question that made them not smell. Apparently I was wrong when the salt/sugar is pure but typical supplies aren't necessarily pure, is what I'm understanding. WasabiFlux's answer has made everyone else on all sides of the debate able to convince themselves that they were right all along. I now have some follow-up questions.

So hopefully not too tangentially:
When people say they smell sweet things, let's use the example of Cinnabon since I can definitively state people have told me that's a distinctive smell, what are they smelling? Is it just cinnamon and they're mentally filling in sweet, or is there a sugar/icing smell as well? Or sweet coffee? I guess what I'm asking is what does "sweet" or "sugar" smell like - is it just other associated smells like vanilla or cinnamon that make people think "sweet" or do all "sweet" examples always involve caramelized sugar?

And, for that matter, it sounds like "ocean" or other smells traditionally described as "salty" smell like other scents that aren't salt? Are people generally confusing the taste of the air at the ocean with the smell when they use the descriptor salty? I guess I always assumed "briny" smelled kind of like it tastes...

(lonefrontranger, I'm the worst person to conduct such an assay** - I did not even know until this moment that tap water smells different from distilled. I mean, it makes sense that you say that, I just never thought about it and like I said, it's all academic to me. Though I'm not sure it should affect the rest of the test since all the beakers would smell like tap but then since people say they can smells carry/suggest/neutralize... maybe it does? I'm getting confused again. Also setting up brands of sugar beyond limiting it to white sugar seems like it means people can differentiate sugar by smell which is part of the question, no? Or perhaps like you said they can just differentiate packaging smells? Anyway, if anyone would like to execute lonefrontranger's or your own thorough assay and report back, I'd be interested.)

*Only my sister is allowed to buy me perfume now, after an atrocious incident in high school where they had to evacuate the classroom and sent me home to effectively deskunk myself from a gifted cologne.

**Also, I got kicked out/excused from high school chemistry lab (still got to do the math parts though) at one point for sitting over an open canister of really strong HCl until I literally burned the inside of my nose.
posted by vegartanipla at 6:20 PM on August 20, 2014

Actually I would argue that you're the BEST POSSIBLE person to run (not partake in! RUN!) such an assay because:

1) you are completely incapable of being biassed by virtue of your unique status.
2) you are incapable of biasing your subjects by same.
3) you have no vested interest in the outcome short of simple curiosity.

Also you cannot be harmed by the ingredients, and the methodology here is a simple one of measurement and weights. You don't have to do any of the smelling, just procure the ingredients and your test subjects, ensure that the methodology and sampling is consistent and record the results FOR SCIENCE!!
posted by lonefrontranger at 6:37 PM on August 20, 2014 [2 favorites]

No seriously. The fact that you didn't know beforehand that tap and distilled water could smell different is a feature, not a bug here. You just have to control the facts, you don't have to participate and in fact, proper clinical protocols demand that you don't - you are merely there to outlay the process of the assay, ensure consistency of sampling, and record the facts.
posted by lonefrontranger at 6:39 PM on August 20, 2014 [1 favorite]

oh right... "ocean" smells like "ocean" not because of the salt, but because of the enormous bioburden of marine life that is present in seawater. Specifically the most concentrated "marine" odor I can describe is a direct result of a certain type of marine algae that is omnipresent in seawater and has been isolated for use in the "nutraceutical" industry (of which I worked for a startup) that formulates DHA for use in food supplements. It oxidizes rapidly in air - when live/fresh it smells like clean ocean and when oxidized / off it smells like dead fish.

Most of the smells you are describing are attributable to "volatile organic compounds" or VOCs - most "sweet" aromas are actually various esters like ethyl propionate which smells strongly of butterscotch. "Cinnabon" is a highly characteristic conglomeration of cinnamon (ester), vanilla (ester) and caramelizing (burnt) sugar, which is partly phenols and a bunch of other stuff I can't recall now.
posted by lonefrontranger at 6:49 PM on August 20, 2014 [2 favorites]