2. Smell (Olfactory Sense)

While the sensation of taste is limited to a few basic (and important) sensations, smell is a cornucopia of data. We’re wired to detect somewhere around 1,000 distinct compounds and are able to discern somewhere over 10,000 odors. Like taste, our sense of smell (olfaction) is based on sensory cells (chemoreceptors) being “turned on” by chemical compounds. In smell, these compounds are called odorants.

In the case of olfaction, the receptor cells are located in the olfactory epithelium in the nasal cavity and respond to volatile chemicals—that is, compounds that evaporate and can be suspended in air such that they pass through the nasal cavity where the chemoreceptors have a chance to detect them. Our sense of smell is much more acute than our sense of taste; for some compounds, our nose can detect odorants on the order of one part per trillion.

There are a few different theories as to how the chemoreceptors responsible for detecting smell work, from the appealingly simple (“the receptors feel out the shape of the odor molecule”) to more complex chemical models. The more recent models suggest that an odorant can bind to a number of different types of chemoreceptors and a chemoreceptor can accept a number of different types of odorants. That is, any given odor triggers a number of different receptors, and your brain applies something akin to a fuzzy pattern-matching algorithm to recall the closest prior memory. Regardless of the details, the common theme of the various models suggests that we smell based on some set of attributes such as the shape, size, and configuration of the odor molecules.

This more complex model—in which a single odorant needs to be picked up by multiple receptors—also suggests an explanation for why some items smell odd when you receive only a weak, partial whiff. To use a music analogy, it’s like not hearing the entire set of notes that make up a chord: our brains can’t correctly match the sensation and might find a different prior memory closer to the partial “chord” and misidentify the smell.


It also appears that we smell in stereo: just as our ears hear separately, we use our left and right nostrils independently. Researchers at UC Berkeley have found that with one nostril plugged up, we have a much harder time tracking scents, due to lack of “inter-nostril communication.”

While you might think of smell as being only what you sense when leaning forward and using your nose to take a whiff of a rose, that’s only half the picture. Odors also travel from food in your mouth into the nasal cavity through the shared airway passage: you’re smelling the food that you’re “tasting.”

When cooking, keep in mind that you can smell only volatile compounds in a dish. You can make nonvolatile compounds volatile by adding alcohol (e.g., wine in sauces), which raises the vapor pressure and lowers the surface tension of the compounds, making it that much more likely that they will evaporate and pass by your chemoreceptors.


Chemists call this cosolvency. In this case, the ethanol molecule takes the place of the water molecules normally attached to the compounds, resulting in a lighter molecule, which then has a higher chance of evaporating.

Here’s a simple experiment that shows the difference between taste and smell. You’ll need a test subject, two spoons, a grater, an apple, and a potato. Without the subject seeing, grate some of the apple (without skin) onto one spoon, and grate some of the potato (again, without skin) onto the other spoon. Have the subject pinch her nose shut, and give her both spoons to taste. Make sure she keeps that nose pinched the entire time! This prevents the air carrying the odorants from circulating up into the nasal cavity. After she’s tried both spoons, instruct her to stop pinching her nose, and note what sensations occur. If you want to do this with a large group, flavored jelly beans work, too.

Temperature also plays an important role in olfaction. We have a harder time smelling cold foods because temperature partially determines a substance’s volatility.

Your sense of taste is affected by temperature, too. Researchers have found that the intensity of primary tastes varies with the temperature both of the food itself and of the tongue. The ideal temperature is 95°F / 35°C, the approximate temperature of the top of the tongue. Colder foods result in tastes having lower perceived strength, especially for sugars. It’s been suggested that red wines are best served at room temperature to help convey their odors, while white wines are better served chilled to moderate the levels of volatile compounds and sweetness. This would make sense—by chilling white wine, it’ll be less likely to overpower the milder meals that they customarily accompany, such as fish.

Jim Clarke on Beverage Pairings

Jim Clarke is a wine writer whose work has appeared in the New York Times, the San Francisco Chronicle, Imbibe, and Foreign Policy, as well as on Forbes.com and StarChefs.com. He is also the wine director at Megu in New York City. Above, Jim stands in front of wood-fired brewing kettles at the Brasserie Caracole in Belgium.

How do you pair beverages with food?

What you’re looking for is the structure of the beverage and the dish. For example, if you have sweetness in a dish, you’re going to want a similar level of sweetness in the wine. If you don’t, the wine will taste relatively flat compared to the dish, or if the wine is too sweet, the dish will be less expressive.

Another example would be acidity. Salads can be very difficult because you have acidities in the vinaigrette dressing, so you need a wine that is going to have that acidity as well, or the wine is going to seem flat or even a little bit bitter next to the dressing. If you want high acidity, you can buy an Austrian Grüner Veltliner, a New Zealand Sauvignon Blanc, a New York Dry Riesling, as a couple of examples. Sancerre are 99% of the time going to be dry and acidic.

If you’re not into learning about different wines in and of themselves, then when you’re buying the wine you should have a retailer who you can talk to. Tell them what the protein is as well as the sauce or preparation. You want to say, “Grouper with a red wine sauce as a reduction: should I do that with a red wine or a white wine?” If you know the dish well and you say, “There’s a really buttery sauce,” then your retailer will probably direct you to a California Chardonnay.

The convention I’m familiar with is to look at the type of wine. It sounds like this is not a bad approach?

It’s not, especially when you talk about Old World wines. A lot of times Old World wine drinkers wouldn’t differentiate. They would say, “I’m making coq au vin, so I need a burgundy.” There are good ones and there are bad ones, but as far as a pairing goes that’s a good pairing. So it can be fairly generic. There is really a broad range of wines within a given category that are going to work pretty well with any given dish.

What are the key variables in wine pairings?

Acidity, tannins if you’re going with a red wine, body or alcohol level, and sweetness are really the four main things. Flavor is kind of a bonus. The aromas aren’t so important to the pairing as the other elements. High alcohol, say California Chardonnay, can be pretty overwhelming for a delicate fish dish. On the other hand, with lobster it’s often fantastic because of lobster’s rich flavor.

Look where a wine comes from; that really tells you quite a bit. In 95% of cases, if it’s somewhere warm, the wine probably has fuller body. If it’s fuller-bodied, then it has lower acidity, because those two have an inverse relationship. Sugar in the grapes eventually becomes alcohol in the wine. Unripe fruit is tart; that’s acidity. As it becomes ripe, it comes into balance. If it’s overripe, it actually tastes kind of plain because the acidity has dropped out. Take a place like California, where there are these beautiful warm vintages. Ask me for a light-bodied California white and I’ve really got to dig on my list. There are a few little isolated areas that do it, but it’s really not what they do best. On the other hand, Austrian whites are generally from a cool-climate growing area; those are usually pretty good in acidity, light to medium bodied, and lower alcohol.

Why do so many people talk about flavor and aroma instead?

People find it much more poetic to talk about the aromas and the flavors. From a practical point of view, if I’m a sommelier on the floor, I’ll be very careful about using the word “acidity” with guests. I’ll use all sorts of euphemisms like “crisp” or “fresh,” because people don’t think about acidity in the context of food. “I don’t want to drink acid! That sounds terrible!” The fact of the matter is that every beverage has acid in some balance with sugar. Coca Cola technically has more acid than any wine you can think of.

It seems like the way that somebody inside the industry talks about wine is not the same language that’s used publicly. Why is that?

If I’m talking to someone in the industry and they say a modern Rioja, I know exactly what they mean, so we skip a lot of stuff. When I’m training servers or people new to the restaurant industry who need to learn about wine, I talk about that cold climate/hot climate thing and then—and this is a little bit harder, because wine making is changing—about Old World versus New World. New World has more fruit expression; Old World has more earth and spice sort of things. It’s still generally true, but there are always exceptions. If someone tells me it’s a classic Napa Cab, I know it’s full bodied because of the warm climate and has more fruit expression because it’s New World. So when we talk, we only have to say how it’s different from that model, whereas when I talk to the consumer, I can’t assume that they have that understanding already.

Are there similar kinds of variables that you use to describe beer pairings?

Alcohol is still a factor, as is sweetness—acidity not so much except in some unusual beers like lambics. You don’t have tannins but you have hops. Those play into how you pair, just like acidity and those other things in wine. One of my favorite classics is oysters and dry stout.

Are there particular things that you would avoid in pairings?

Don’t go overboard trying to get the right pairing, especially if you have a style of wine or beer that you really don’t like. People will say, “I’m trying to eat fish because it’s healthier, but I love red wine.” Well, don’t let that stop you. I drink all sorts of wine depending on the occasion or how I feel, but if I’m not in the mood for a big red and I’m having a steak, I’ll find something else. You need to match with your own tastes along with matching the food. Certainly, as a sommelier, the first thing I’m trying to find out is not what the guest is having, but what they like. Pairing is to give you more pleasure.

Any tips for a consumer speaking with a sommelier?

Well, certainly telling sommeliers what you like. Also, a lot of people feel like they need to dance around price. There is an easy way to do this if you’re entertaining guests and you don’t want to make a big show of not spending a lot of money. When I’m talking to a guest I will have the list open right there so they can run their finger along the name of the wine to the price. They tell me what they’re interested in spending. If you wanted to say, “We’re looking for something around $100,” that’s fine, too, but this is kind of a genteel way of doing it. This will save a lot of the feeling like we’re sparring with each other because now I know what you’re looking for, both in style and in price range, and we’ll find a wine for you.

Is there an exercise that one could do to better understand how to do wine pairings?

Get four glasses, one with lemon juice and water, one with very overbrewed ice tea, one with some sugar dissolved in water, and one with half vodka, half water. Then get a few dishes or ingredients and taste each of them with the different elements—tasting with lemon juice, the sugar water, the tannins in the tea, and then alcohol. You can see what each individual element is doing to, say, a piece of cheese. What is each doing to this piece of asparagus? You’ll see what those different elements are and how they affect the food. We’re not talking about wine flavors at all, just the four elements that occur in wine that are really important to the pairing process.

Smelling Chemicals

Our noses are veritable chemical detectors on par with modern lab equipment. Our sense of smell is capable of distinguishing the difference a single carbon atom makes (e.g., octane versus nonane) and sniffing out compounds all the way down to the level of 0.00002 parts per billion (for one compound in grapefruit). That said, factors such as age, hormonal levels, and exposure mean that some of us notice smells at lower thresholds than others.

Not all compounds can be smelled. Size, shape, and something called chirality all determine whether a molecule is smellable or not. Chirality has to do with whether or not a molecule and its mirror version (the pair is known as enantiomers) are identical. Your left and right hands, for instance, are chiral because they are not identical, even though they have the same fundamental shape. Carvone is a classic example in chemistry: the compound D-carvone smells of caraway, while R-carvone smells of spearmint.

Some chemical structures have distinct smells, and the families of compounds that contain those structures generally end up smelling similar. Esters (compounds with the general formula of R-CO-OR’) are classically thought of as having fruity aromas. Amines smell stinky and rotting, like week-old raw fish, with cadaverine and putrescine being two of the more well-known odors. And aldehydes (organic compounds that have a carbon atom both double-bonded to an oxygen atom and bonded to a hydrogen atom) tend to smell green or plant-like.

While smelling an aldehyde won’t bring the entire smell of, say, green ivy, it’s similar enough that industry can use aldehyes as artificial odorants to trick our brains into thinking we’re smelling the real thing. Artificial flavorings are used in products from laundry detergent to candies, because they cost less and in some cases are chemically more stable than the original scents. Artificial vanilla extract, for example, generally contains just vanillin, which has the molecular formula C8H8O3, which happens to be the most common chemical in vanilla. Although the artificial stuff is missing all the other compounds from vanilla, we still find it to be enjoyable.

Many other herbs and spices are also composed of just a few key chemicals, making artificial extracts of them relatively close to the real thing. Fruits, however, have hundreds of compounds that are involved in creating their aromas. Even adding the dozen or so most common chemicals for an artificial strawberry flavoring, for example, leaves 200+ volatile compounds missing in the “odor spectrum.” This is why artificial fruit flavors tend to taste, well, artificial (chocolate, too).

Here are a few examples of compounds and their smells. A number of these compounds can be purchased online if you happen to have an account with an industrial supplier, such as sigma.com. (Make sure you acquire food or medical grade versions!) Flavored jelly beans and scratch-and-sniff stickers are just a few products that rely on these compounds, so if you don’t just happen to have an account with an industrial supplier, try popping open a package of jelly beans and seeing if you can identify some of the odors with these compounds.

2,4-dithiapentane: Black truffle

Black truffle oils commonly use this in lieu of oil from real truffles.

Isoamyl acetate: Banana

Creating artificial banana extract is one of the classic chem lab projects, to the annoyance of teachers in adjoining rooms. It’s also the pheromone that honey bees use to signal attacking, so don’t take overly ripe bananas on a picnic during the height of bee season.

Benzaldehyde: Almond

Primary component of bitter almond oil.

Diacetyl: Like butter

Used in microwave popcorn and Jelly Belly’s “Buttered Popcorn” flavor, in large doses it causes a lung disease called “popcorn lung.”

Furaneol: Strawberry

Also occurs in pineapple, tomatoes, and buckwheat.

Hexanal: Generic fruity flavor, “tutti frutti” (like pink bubble gum)

Search Sigma.com for 115606-2ml. Used in Jelly Belly’s “Tutti Frutti” flavor.

Hexyl acetate: Golden Delicious apple

Search Sigma.com for 25539-1ml.

Maple lactone: Like maple syrup

Search Sigma.com for 178500-10g.

1-p-menthene-8-thiol and nootkatone: Grapefruit

Grapefruit has at least 126 volatile compounds, but these two seem to be the primary ones. Jelly Belly’s “Grapefruit” flavor likely includes this compound.

Then there’s the effect of the temperature of the tongue itself. For example, when drinking a cold soda, as you consume more and more of it, your tongue will begin to cool down. And as your tongue cools, you should perceive the soda as being less sweet. There’s a reason why warm soda is gross: it tastes sweeter, cloyingly so, than when it’s cold. What does all this mean when you’re in the kitchen? Keep the impact of temperature on your senses of smell and taste in mind when making dishes that will be served cold. You’ll find the frozen versions of things like ice cream and sorbet to be weaker tasting and smelling than their warmer, liquid versions, so adjust the mixtures accordingly.

As an example, try making the following pear sorbet. Note the difference in sweetness between the warm liquid and the final sorbet. Yes, you could just buy a container of sorbet and let some of it melt, but where’s the fun in that?

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