3 Good Taste

Concepts

Appetite

Smell / scent

Taste / flavour

The smell-taste connection

Scent, immunity, and memory

Fooling our sniffers

Chew your scents: the retronasal system

Flavouring agents

Rules of eating well

“Tastes like shit, but you can live on it.”

—Crocodile Dundee

“Mechanically, dispirited after a dreary day with the prospect of a depressing morrow, I raised to my lips a spoonful of the tea in which I had soaked a morsel of the cake. No sooner had the warm liquid mixed with the crumbs touched my palate than a shudder ran through me and I stopped, intent upon the extraordinary thing that was happening to me. An exquisite pleasure had invaded my senses, something isolated, detached, with no suggestion of its origin… I had ceased now to feel mediocre, contingent, mortal. Whence could it have come to me, this all-powerful joy? I sensed that it was connected with the taste of the tea and the cake, but that it infinitely transcended those savours, could not indeed be of the same nature. Whence did it come? What did it mean? How could I seize and apprehend it?”

—Marcel Proust, Remembrance of Things Past, 19131

In Chapter 2, we looked at the common distinction between healthy and tasty. Again, we often assume that “healthy” and “tasty” are opposite things – that “healthy” foods must taste bad (or at least, less good); and what’s “tasty” must not be healthy.

I argued that in fact, the tastes and textures we’re primed to like – sweet, fatty, and salty – are healthy tastes… in their original form. Modern food products available with those tastes – along with the helpful input from food companies who remind us that their blueberry danishes taste much, much better than real blueberries – lead us astray. Our 10,000 year old taste buds haven’t caught up to our 21st century fake foods.

But what is taste? Where do flavours come from? And how do these relate to our appetite and to our bigger project of eating well?

In this chapter, we’re going to snuffle and slurp our way to understanding how flavours and our experiences of those flavours affect what we like to eat, and why we eat it.

ConceptsLet’s review a few concepts.

AppetiteAn acquaintance of mine once told me that in his native language, the word for “appetite” translates roughly as “I feel like eating”.

Appetite isn’t hunger – it’s the desire to eat. Hunger is a physical sensation: a growling stomach, lightheadedness, the shakes, etc. Appetite is a mental, emotional, and psychological state.

Appetite is wanting.

Have you ever experienced these situations?

It’s the end of a big Thanksgiving dinner. You’re stuffed. The thought of one more piece of turkey makes you want to upchuck. Hey – Grandma’s dessert is here! Yummy!

You’re rushing to an errand. You walk past a bakery and catch a whiff of fresh baked bread, or the seductive scent of burnt sugar and vanilla. Like a robot, you go on autopilot and forget briefly about the errand – time to grab a bite!

You’re at the office, hard at work on a boring project. You’ve just had lunch. Someone sends round an email: “Homemade brownies in the lunchroom!” From that point forward, you cannot focus on the project. The brownies are calling your name.

Dinner and a movie – the classic date. And what would a movie be without a big bucket of salty, buttery popcorn?

You’re hungry. You open the fridge and rummage a bit to see what’s there. There’s lots of healthy food, but nothing appeals to you, so you simply wander away. Later, you order pizza.

What do these situations have in common? Either your hunger was out of sync with your appetite, or you were easily prompted into wanting to eat by the sight, smell, or mere thought of food. The foods that grab your appetite’s attention are, of course, likely foods that are sugary, fatty, and/or salty.

Notice that in all cases, whether you were actually hungry was somewhat irrelevant. Either you wanted to eat more when you were already full, or you didn’t want to eat something when you were truly physically hungry.

Also notice that your appetite often depends on what you think or feel.

Maybe you want to eat when you’re happy, stressed, bored, sad, tired, angry, etc. Maybe you want to eat Grandma’s dessert because it gives you comfort and makes you feel attached to your history. Maybe you want to eat that popcorn at the movies because you always eat popcorn at movies. And dang, it smells good when you enter that theatre lobby.

Thus, your thoughts, feelings, memories, and habits all strongly affect your appetite.

However, other physiological factors can affect your “wanting-ness”. Two of the most powerful are smell and taste. We’ll look at other factors in subsequent chapters.

Smell / scent“My dog has no nose.”“How does he smell?”“Awful.”

—Monty Python, “The Funniest Joke in the World”

Fresh-brewed morning coffee. Pumpkin pie. Smoky barbecue. A fish market.

You can almost smell these just by reading the words, can’t you?

The first three probably made you think: mmmmm. The last one: euww!

Unlike many animals, humans’ sense of smell is comparatively weak (which probably saves us from some awkward moments of crotch-sniffing when meeting new friends). Yet we share a common past with our animal cousins, which means that the primal structures of our brains are very much alike. Whether you’re a mouse or a man, those two holes on your snout are used for more than just storing snot or snorting coke.

In this chapter, I’m going to talk about how our sense of smell drives our appetite.

I’ll use the terms “scent” or “odour” (and possibly “funk”) to describe chemical aromas and volatile compounds given off by foods. I’ll use the term “smell” to describe the act of inhaling and interpreting those aromas. Scent is the noun, smell is the verb.

I’ll also describe the act of smelling as “olfaction” and the system that lets us do that smelling as the “olfactory” system, both of which come from the Latin olfacere: sniff.

Taste / flavourIn the case of taste and flavour, flavour is the noun, and taste is the verb. Flavour is something that a food has. Taste is something that we do.

A fancy word for “taste” is gustation, from the Latin gustare – to taste.

By the way, the etymology dictionary tells me that gustare and its cousin gusto comes from the approximately 5,500 year old Proto-Indo-European base geus, possibly related to the Sanskrit word jus ("enjoy, be pleased"), the Avestan zaosa ("pleasure"), and the Old Persian dauš ("enjoy"). This is the linguistic root of words for "taste" in Greek and Latin, but in the Germanic/Old English branch of the Indo-European family, suggests something more like "try", "choose", or “test”. Nobody knows for sure, but this all suggests that the common concept of “taste” is something like choosing or testing something that is ideally pleasurable.

Even more interesting is that Latin root for words describing knowledge and wisdom – sapere, which gives us Homo sapiens, or wise humans – can also imply taste and smell. Sapere is defined thus:

1. to know information (knowing what)

2. to be able to, can, could (knowing how)

3. to taste, to smell

4. to come to know; to become informed of; to find out.

Could taste and smell thus be understood as a way to seek, try, and know pleasure?

The smell-taste connectionEver had a cold and lost your appetite because you couldn’t smell anything? Food just tastes blah when you can’t smell it.

On the other hand, have you ever caught yourself salivating at the mere scent of food? Even before we see the food, our digestive system knows a delicious aroma means “food’s near!”

Our sense of smell and our sense of taste are very closely related.

For one thing, they both come from the same food chemicals: volatile compounds that somehow interact dynamically with our sensory apparatus. In other words, scents and flavours occur because something in the food interacts chemically with receptors in our bodies.

Volatile means that the substance reacts with things instead of just staying inert. Compounds are mixtures of chemicals. Thus, a volatile compound is a collection of chemicals that somehow reacts with something else, sort of like a really annoying loud guy wearing an ugly Hawaiian-print shirt and smoking a smelly cigar, who gets on everyone’s nerves no matter where he goes. (An

inert compound would be more like that mousy wallflower whom everyone thinks is more or less nice, but they can’t quite remember her name and nobody notices when she leaves.)

This ability to detect, identify, analyze, interpret, and respond to volatile compounds is known as chemosensitivity or chemoreception.

While we don’t have the acute scent perception of many animals, we’re still pretty darn good at it. We can detect and distinguish thousands of scents, often much better than even the most sophisticated “sniffer” machines.

[Expand on this] Appetite hormones along with insulin etc. have receptors in the olfactory bulb. Diabetes and increased glucose impair olfactory function.2 Orexogenic hormones tended to increase and anorexogenic hormones tended to decrease olfactory sensitivity, modulating olfactory performance in a similar way as fasting and satiation.3 In both morbidly obese and anorexic patients, olfactory function was found to be impaired.4

The structure of our bodies also puts smell and taste together. Your nose is above your mouth for a reason, and not just so you can impress potential mates by touching your tongue to your schnoz. It’s quite convenient and probably no accident that our important orifices are organized together. Imagine your nasal passages and mouth as two cavities stacked on top of each other, like the letter “8”. These cavities contain very finely tuned sensory organs that work in concert.

Orthonasal olfaction means stuff that we smell through our nostrils. When you delicately place your nose into a bouquet of roses sent by a secret admirer and inhale, that’s orthonasal olfaction. (Perhaps the admirer is impressed by the fact that you know the phrase “orthonasal olfaction”. It certainly turns my crank.)

Retronasal olfaction means stuff that we smell through our throats. Umm… huh? Remember that episode of Jackass where Steve-O snorted an earthworm up his nose, then horked it out through his mouth? Or that time someone made you laugh while you were drinking, and the liquid came out your nose? Same idea. Our nasal passages connect to our throat at the back, so we can smell things that are in our mouths or become reality TV stars.

Both ortho- and retronasal olfaction are important. They help us identify, analyze, interpret, and judge foods.

(By the way, there’s another “—nasal” system: the vomeronasal system. This system senses compounds such as pheromones, which are subtle signaling chemicals between organisms. Pheromones tell Fido the dog that Fluffy has peed on the same fire hydrant, or tell the killer bees to attack you all at once. Humans have a vestigial vomeronasal system, but we don’t know yet how much it affects our behaviour. This hasn’t stopped cheezy back-of-magazine advertisers from promising lonely men that they’ll attract beautiful women with the Magic Pheromone Cologne.)

For our own survival, we need to know things like Is this food safe to eat? Will it taste good? We know that if it smells or tastes bad, we shouldn’t eat it. We also need to remember food choices that we’ve made earlier.

Thus, smell and taste don’t just let us know whether chocolate truffles are yummy. These senses (like all senses) protect us from harm.

Scent, immunity, and memory“From the prebiotic history, nutrition and immunity of the cell are mutually interacting processes aiming at the same goal – namely to survive.”5

Here is a paradox: Our immune system fights foreign substances. Yet food is fundamentally a foreign substance.

We have to take stuff from the outside and put it into our insides. This is always risky. Food can carry disease-causing pathogens. Food itself can be a pathogen. (More on this in Chapter 4.)

We need food to survive. We must also keep ourselves safe from external invasion.

Both our digestive and immune systems:

want to make foreign substances (i.e. food components) safe, harmless, and useful

break down big chunks to little chunks; large molecules to smaller ones

use the delicate outer linings of tissues – aka epithelial membranes – and a mucosal layer that works as a selective barrier to keep bad stuff out and let good stuff in

are very, very picky about what they’ll recognize and allow – right down to the specific shape of foreign molecules

use the complex processes of detecting, identifying, and interpreting smell – aka the olfactory system – as the first line of recognition and defense

Yet again, here’s our paradox. Feeding and protecting are essentially two contradictory, yet mutually interacting processes.6

What’s a body to do?

For one thing, organize a “first responder” team that identifies, sorts, and decides what to do with any new information, whether that “information” is energy (such as sound or light), chemical (such as smell or taste), or mechanical (such as touch).

Food is like a package of information. Our digestive systems, starting from the stomach on down, handle a lot of what’s inside the package. The information contained in the package tells our bodies to do things, such as make proteins or energy.

But before the package gets fully opened, our senses of smell and taste decide whether the wrapping paper is ugly, rip the wrapping off, and peek inside the box.

Remember in Chapter 2 we talked about how good tastes were healthy during our Paleolithic days? The same idea applies here. Sweet flavours and pleasant scents usually mean “safe to eat” – at least, they did 10,000 years ago, when a sweet flavour was a fresh-picked guava and a pleasant scent was a fresh-killed mammoth steak roasting over a fire.

Quick! Name the 1994 Nobel Prize for Physiology and Medicine! What? You don’t know? Do you live under a rock or something?

Well, while you were watching OJ Simpson’s white Bronco on the run from the cops, Alfred G. Gilman and Martin Rodbell were accepting the award for their work on G-proteins. (Oddly, the TV ratings for this one weren’t as good.)7

G-proteins are like telephone exchanges in a cell. They get messages from receptors, and then pass the message on to somewhere else.

One of the main functions of G-proteins is to receive and transmit sensory information to our brains. For example, we have G-proteins in:

the rod and cone cells of our eyes

our nose

our taste buds

G-whiz those G-proteins are G-reat!

In order for us to smell something, a scent (aka an odorant compound) interacts with our sniffing equipment (aka olfactory receptors).8 This sends a signal to olfactory G-proteins, which say, “Hey,

there’s something interesting here – pay attention!” Sensory neurons say, “Hm, OK, let’s kick this upstairs to the boss.”

Different odorants are assigned to different neurons, so all the boss (aka the brain) has to do is look at which neurons were activated. In a sense, each unique scent has a “shape” – a specific pattern of neuronal activation. G-proteins are important intermediaries in this process. Through their “switching function” mechanism, they tell the neurons that there’s something worth noticing.9

Well, that’s cool and everything, but why do we have olfactory G-proteins in the first place?

One explanation is that olfactory G-proteins underlying odour perception (and possibly taste) originally evolved as a defence mechanism against dangerous foreign substances and their originators. G-proteins and immune-related molecules are like sentries – they’re part of the first line of defense against dangerous elements in our environment.

Being able to smell something bad before we ever come into contact with it is a pretty useful ability. If we swallow those rotten eggs, for instance, our digestive system will have to work much harder to keep the pathogens from invading our bodies. But if we can catch a whiff of eggy stench first, we’ll know that we should move on and look for a fresher specimen.

In addition, because the olfactory nerve that connects our sniffer to our thinker is pretty much a direct route between nose and brain, it’s also an easy route for pathogens such as viruses to travel.

(When scientists discovered this in the 1930s, they decided it was a swell idea to wash out children’s noses with alum, picric acid, or zinc sulfate in order to prevent polio. This worked, sort of, but it also left many children with permanent anosmia – no sense of smell. And you thought getting your mouth washed out with soap was bad!)

Thus, evolution has equipped our smelling and tasting structures with things that thwart foreign invasion as much as possible. In particular, this includes cilia (teeny tiny nose hairs, which act like a filter and a broom) and various chemicals such as enzymes that inhibit pathogens.

Evolution, being a belt-and-suspenders kind of process that likes redundant backup systems, has also gone beyond chemical defense into behavioural and cognitive defense.

Smell is strongly linked to memory, both psychological and physiological. The olfactory system is connected closely to a region deep in the brain known as the amygdala.10 This region is like a bridge between thinking and feeling, especially in our relationships with other people and our environment, and it’s strongly self-protective.

For instance, the amygdala helps store memories associated with emotionally significant events, especially fear. It may also help us judge the threat level of social interaction. People whose amygdalae are damaged don’t respond to people invading their personal space.11 Such people also have trouble naming and recognizing odours. Our amygdalae are much more active when we smell something bad.12 Thus, if our amygdalae are not working properly, we are vulnerable.

There’s also some evidence that olfactory G-proteins are involved with regulating dopamine and adenosine in the striatum, which suggests that…13

This connection between olfaction, social recognition, and self-defense means that smell is a powerful memory-maker.

In a sense, one job of our immune system is simply to create, collect, and classify memories.

Our innate immune systems have a “pre-fabricated” memory. They don’t really care what bad thing comes at them – they just know their job is to block and kill it. Their “memory” is more like a script they get more or less from birth.

Our adaptive immune systems make new memories. When we’re exposed to a pathogen such as a virus or bacteria, we learn and memorize the shape and characteristics of that pathogen, so that if we ever see it again, we can really kick its ass.

By the time we’re old, our immune system is really darn cynical. It’s seen so much action, it hates pretty much everyone.

Thus, memories can involve storing and recalling mental information such as your first kiss, trip to Paris, or deadline for the TPS reports. But memories can also be physiological. Memories tell us what do to with things.

As a university student, I spent one evening chugging a mickey of Jack Daniels at a party. As my drinking buddies and I got progressively more inebriated, we made and consumed bag after bag of microwave popcorn. The next morning, I crawled out of bed, over the popcorn-littered floor. The scent of fake butter hit me like a brick wrapped in a wet towel. I barely made it to the toilet before projectile vomiting. I think I puked for about 24 hours straight. My advice to you: don’t play drinking games with engineering students.

For years afterwards, the smell of buttered popcorn made me want to throw up. And I could not recall the “JD incident” without feeling tummy butterflies, which signifies the important role of the enteric nervous system, aka the gastrointestinal tract’s “second brain”. More on that in Chapter 4.

Maybe you too ate or drank something that made you sick and now you can’t stand the smell or taste.

Memory is sort of a biological shorthand as well as a program of action. It helps us rehearse and prepare a specific reaction to a specific situation. If we associate toxicity with a characteristic smell, we’ll avoid that smell in future. Experiments have shown that people can be made to associate a particular smell with getting sick. If I make you smell roses before making you barf, then eventually, you’ll retch every time you get those roses from the secret admirer.

However, luckily (or unluckily, depending) it seems that we have different orthonasal processors for food aromas and non-food aromas. You’re still more likely to associate digestive phenomena with food than flowers.

This smell-memory connection works both ways: It lets us know what to avoid, but it also lets us know what we like. It’s particularly powerful if scent memories are established when we’re young. This explains why childhood associations are so prevalent in comfort foods. We remember the scent of Grandma’s cookies, or the smoke of summer campfires as we toasted marshmallows, or street food from the market in the old country. And we’ll seek those things out – as well as the feelings those things give us – as adults.

The point of smell-taste-memory, then, is to help us eat well.

One interpretation of “eating well” is that it refers to actually eating skillfully – doing a good job of the eating process. Ideally, this means we don’t eat things that are poisonous, and we prefer foods that are nutritious. As one researcher writes, “Ideally, persistent biochemical memories and olfactory preferences serve to coordinate a habitual physiological state with a successful set of food choices in an environment.”14 (Same idea, more academese.)

Smell and taste, working together with our memory systems, help us identify and describe things as we encounter them. We look at the food, touch it, taste it, smell it. We feel and think things before, during, and after eating. We experience physical sensations of digestion. We eat in a particular social context.

We can interpret and synthesize our previous smell-taste experiences – as well as all these other elements – into memories. Memories shape our preferences and our behaviours. This means memories affect our appetite – our desire to eat – and our food habits.

By the way, we can think of memory as extending beyond the individual, into our genetic heritage. Recent work in the field of epigenetics (processes that affect inheritance without actually changing our genetic code) shows that our ancestors’ food environment can affect the expression of our DNA.

For instance, if our mothers survived a famine while pregnant with us, we’re more likely to be overweight or obese. Our genes didn’t change, but our bodies’ expression of those

genes did. Certain “famine resistant” genes got switched on, which means that we put on weight more easily, just in case another famine comes knocking. This epigenetic heritage appears to persist through several generations. Add that to your mother – and grandmother – issues to discuss with your shrink.

Fooling our sniffersAs we started to ask in Chapter 2, what happens when we break the link between food scent, flavour, and nutrition? One possibility is that we start to “mis-remember” whether foods are good for us.

10,000 years ago, what you saw was what you got. Meat was meat. Plants were plants. Fungi were either delicious, deadly, or a helluva party.

In the 21st century, we can’t count on our normal food cues. That package of food information is often wrapped in different paper. Outside it may look shiny and beribboned, but inside, the box is empty – or worse, it’s one of those novelty snakes that leaps out at you. At this point, our food packages are so disguised, they’re practically wearing a Groucho Marx nose and mustache.

The problem of food packaging is a literal one as well as a metaphorical one.

Metaphorically, our ability to judge whether foods are “good” is compromised by artificial colours, flavours, and scents. Food manufacturers can easily create virtual chemical realities for us. Food labs can create any scent or flavour you want in a test tube, with incredible precision. Forget about the sickly-sweet “grape scented” Mr. Smelly markers you used as a kid in the 1970s; chemists can now make the scent of a 2002 oak-aged Chardonnay from a single postal code in the Napa Valley.

Retailers often use these scents to stimulate us subconsciously, even going as far as pumping them into the ventilation system in the hopes that we’ll be driven like snuffling lemmings off the cliff of mass consumption.

Manufacturers can also cover up or deodorize bad scents such as rancid oils. For example, fatty acids such as omega-3s are chemically unstable and easily go bad. They must be eaten fresh and cold – ideally, in their original form. However, to make fake food products such as margarine, soymilk, or I Can’t Believe It’s Not Butter spray, manufacturers have to use aged or heat-processed oils. In order to eliminate the stomach-churning stench and weird colours of rancid oils, these products have to be bleached and deodorized. The end product, a groteseque zombie-like food creature of artificially resuscitated materials, is kind of like entering a room after a cigar smoker has sprayed Lysol to cover the smell: You end up inhaling both cigar smoke particles and disinfectant. However, thanks to the magic of manufacturing, you think you’re smelling the great outdoors. (Or at least, lavender with a weird cigar smoke afterburn.)

Thus, if the “package” fools our sensory interpreters, then we eat things that are not actually good for us. We are also tricked into wanting more of these things, because they lie to our brains. These fake scents wheedle and coax our brain into accepting them, because the ersatz odours are great pretenders, and they’re so darn appealing. They know just how to find our brains’ soft underbelly and exploit it.

As a result, if we eat fake food, we can’t rely on our senses to help us judge its quality. Fake food fools us.

“[A]griculture itself is inadvertently being designed to uncouple composition from sensory cues. The quantity-based agricultural model, where the relative content of food energy per acre corresponds to a driving force for genetic breeding and agricultural practices, is not necessarily consistent with the content of nutrients that underlie food quality. [P]rocessing that disassembles commodities into component biomolecule classes (proteins, carbohydrates, and oils) serves to further dissociate sensory cues from the composition and quality of foods.” (German 29)

Literally speaking, food packaging is also a challenge. Food perception is especially important now that we have so many food choices. 10,000 – or even 500 – years ago, we basically had two food choices: eat it or starve. Now, our choice of breakfast cereal alone reaches well into the

double digits. It’s crucial that we re-learn how to judge food, and understand that our senses can mislead us.

Manufacturers present food that looks incredibly good… at least in theory. (Who hasn’t, after all, been disappointed by the soggy meat puck that is the reality of a McDonald’s hamburger?) Apples are shiny and bright red. Tomatoes are plump, firm, and ruddy. There’s nary a bug spot or irregularity anywhere to be found. Steaks, having been whiffed through a carbon monoxide bath and pounded by artificial tenderizers, are lusciously pink and tender.

Yet such visual appeal hides food safety problems that our sniffers can no longer effectively detect. In late December 2009, National Steak and Poultry in Oklahoma had to recall nearly 250,000 pounds beef products potentially contaminated with E. coli O157:H7.15 The mechanical tenderization process, in which small needles or blades are inserted deep into the meat, meant that surface bacteria were essentially being injected deep into the meat. Anyone eating a rare-cooked steak was in danger. Consumers were likewise panicked by salmonella in tomatoes, spinach, organic fresh juices, and peanuts.

Packaging also hides the fact that things that look and smell nutritious aren’t necessarily so. Nutrient quality of many foods has declined as soil nutrients are depleted, and farmers rely increasingly on chemical fertilizers. Genetically modified organisms are bred for yield, productivity, and a short time to harvest – but rarely nutrition, and even more rarely taste.

Factory farms use specially bred chickens that mature rapidly, with breasts so big they look like bird exotic dancers and skeletons so deformed they can’t walk properly. Or they grow cows who produce so much milk that they must supplement with massive amounts of calcium so that the cows do not die. In both cases, the products of these animals are laced with antibiotics (and consequently antibiotic-resistant bacteria) and other medications. Fast-growing chicken breasts and their processed offspring (such as deep-fried chicken “fingers”) are pleasingly pale. But in fact, it’s the darker meat that signifies the presence of vitamins and minerals. Organic, pasture-raised heritage chickens usually have darker flesh. The inside of a chickeny-scented nugget has about as much nutrition as styrofoam. It might have a few grams of artificially assembled protein, but it’s missing everything else.

How do we solve this problem?

First, we must understand how essential scent is to our judgement of food. As we make food choices, we should ask ourselves what role scent plays in our decisions. For example, if we choose foods because they remind us of things that are comforting, we should ask ourselves what we’re really looking for in the first place – physical nourishment or a memory of security and love?

Second, we must learn to smell effectively and intelligently. Yes, I know you already know how to smell things. But do you really? Are you conscious of what you are smelling? Can you name scents? When you eat, do you take the time to reflect on the food’s scent? Compare the scent of the real thing (e.g. an orange, a cucumber, or a melon) to its imitator (e.g. orange drink, cucumber-melon gum) and see what you notice.

Third, we must recognize that food manufacturers know that scent is important, and they will use that knowledge to mislead us. If we’re eagerly chowing down our third Big Mac and strawberry shake, we should consider the possibility that our sniffers are being misled into thinking that this is a good idea (or that this is food in the first place).

Fourth, eat real food. Real food, food that is whole, unprocessed, and “close to the ground” is what we evolved to eat. As you get re-acquainted with it and take the time to experience it, you will notice that its scents are more complex, subtle, and robust than even the best fake food can accomplish.

Fifth, when you smell something good and suddenly want to eat, ask yourself, “Why do I feel this?” Are you genuinely hungry? Or do you just “feel like eating”?

Finally, use your natural olfactory systems as they were designed to work – as a means to help and protect you. These systems can be fooled but they aren’t stupid. Smell and taste thoughtfully and consciously. Understand that smell and taste systems are there for your survival, so it’s in your interest to help them do their jobs. In the next section, we’ll look at how the retronasal system can help with this task – and how more food smelling can help you eat better.

Chew your scents: the retronasal systemThe ortho- and retronasal systems work together. Orthonasal olfaction is most involved in anticipating and wanting food. Retronasal olfaction is most involved in consuming and receiving food. Orthonasal systems deal largely with the perceived reward of food, while retronasal systems deal largely with getting that reward.

These two systems make up what is known as the cephalic phase of appetite. [check this]

When food goes into our mouth, a few things happen.

1. Temperature.

If the food is cold, our mouth warms it. If the food is hot, we cool it down a little. Either way, we get it to a manageable temperature that’s warmish. The warmth of the food enhances the volatility of the compounds, and scents are more easily released.

2. Touch

Touch receptors on the tongue and in the oral cavity sense the texture and viscosity of the food, which is often known as “mouth feel”. We are exquisitely attuned to mouth feel and can distinguish very tiny differences between foods, especially if we’re trained to do so.

3. Air circulation

Along with a bit of food, some air usually gets into our mouths. This air circulates and mixes with the food’s compounds, then wafts up the back of our throats into the retronasal passages. Or, we can deliberately swallow the air to impress our seven-year-old friends by belching.

4. Chemical breakdown

Enzymes in our saliva immediately start breaking down the food, especially the starches. We also have lipase in our mouths, which breaks down fat. This may help us sense creamy and fatty textures and components. More on saliva below.

5. Mechanical breakdown

If necessary, we chew the food to break it down mechanically, which also helps our saliva break it down chemically. A highly coordinated set of nerves and feedback organize this process. Chewing is such a basic act that it’s controlled by our brainstem.16 So, even if you get accidentally lobotomized, you’ll still be able to gnaw on things!

6. Swallowing

As we mash the food up into a bolus (basically a ball of food), push it to the back of our mouths, and send it down the hatch, we transfer the food across our tongues, and its aromas up into our retronasal passages.

These things have two primary purposes: to start the process of digestion, and to enable our chemoreceptors – our smelling and tasting apparatus – to evaluate the food. Warming, aerating, chemically converting, and grinding food helps break it down and release scent and flavour compounds. These scent compounds travel up into our retronasal passages, helping us evaluate and interpret the food. And the scent compounds change as we process and swallow the food.

Have you ever wondered why the first morning sip of coffee is the best one? It’s because coffee aroma actually changes as we drink and swallow it. (German et al) Here’s the process.

1. You take your first sip of coffee. The temperature in your mouth rises. Since heat helps diffuse scent (aka thermal conduction), the volatile compounds in coffee rapidly rise into your retronasal passages. As you work your way through the coffee, the stuff at the bottom of the cup will smell and taste subtly different because it’s cooler.

2. The volatile compounds available rapidly peak, then decrease as your saliva dilutes them. Each compound decreases individually, depending on its unique chemical configuration. Thus, some scents and flavours leave quickly while others hang around.

3. Some compounds diffuse into the mucous layers of our mouth.

4. Our breathing affects the air circulation; thus our perception of the scents and flavours depends on how we drink. Fast chugging will send the compounds through quickly, without giving us much time to perceive them. Sipping and slurping will slow the scents and flavours’ passage. Since coffee is a hot liquid, we’re more likely to sip and slurp it, which draws air in with the liquid – also enhancing the scent and flavour perception of the initial sips because they’re warmer. (You may notice that wine tasters will swish and sort of gargle wine – it looks goofy, and can lead to awkward wine drooling moments, but burbling air through the liquid helps release the flavours in the wine.)

5. When you swallow the coffee and then exhale, that exhalation is known as the “swallow breath”. It’s expelled through the nose and the mouth, which means it passes through the ortho- and retronasal systems again. The compounds in this “swallow breath” are similar to but measurably distinct from the first sip.

6. The “swallow breath” is also different from the post-drinking breath that appears later, with a finishing or after-odour aroma.

Wow! And you thought that you were just waking up in the morning! By the way, decaffeinated coffee will have a different scent and flavour profile than regular coffee, because certain compounds “bleed out” during the process of decaffeination.

Perhaps not surprisingly, people who like coffee unconsciously try harder to experience these aromas than those who don’t. Coffee lovers will spend more time preparing and mindfully drinking the coffee. They’ll pay more attention to the scents and flavours. People who just tolerate coffee as a caffeine delivery system are more likely to slug it back without thinking much about the experience.

This also holds true at a higher cultural and social level. Social groups with a sophisticated “coffee culture” are much pickier about the quality of their coffee and will devote much more energy to brewing and experiencing it. For instance, the traditional coffee ceremony in Ethiopia can take hours and involves careful hand-roasting, grinding, brewing, and serving in small cups for optimal scent and flavour.

This provides us with clues about how to eat well. If we pay more attention to the scent of our food throughout the process of eating, will that improve our food quality and eating experience? The evidence says yes.

While both the orthonasal and retronasal systems function as “food judges” that let us know whether foods are good or bad to eat, the retronasal system is also involved in the digestive process – in particular, helping us to feel full.

We usually think about satiety, or our sense of satisfaction and fullness, as having to do with our stomachs. If our tummies are full, we feel it’s time to stop eating. (And for some of us, the signal “stop eating” is undoing the top button on our pants.)

But there’s some evidence that satiety starts to take shape even before the food hits our stomach.

A recent study explored the relationship between smelling, tasting, and satiety (the sense of being satisfactorily full).17 We might assume that satiety is a “natural” (and thus unchanging) feature of our physiology, but in fact satiation is very much a learned behaviour. We can learn to be satisfied with less food. Or we can learn that we should leave each meal feeling stuffed.

It seems obvious that excessive eating doesn’t do us much good. Thus eating well involves learning (and often re-learning) how to eat so that we nourish ourselves adequately, but don’t overeat.

There are many ways to increase satiety, which we’ll look at more in Chapter 4. However, this research tells us that the more we can smell our food, the more satisfied we are with it.

The study, which examined how satisfied people were with eating different types of foods, found that more retronasal stimulation meant that people were more satiated with less food.

Other studies have found that “Increased insulin levels lead to a reduced smelling capacity, potentially reducing the pleasantness of eating. Therefore, insulin action in the olfactory bulb may be involved in the process of satiation and may thus be of interest in the pathogenesis of obesity.”18

Since retronasal aroma release depends on food structure, composition, and oral processing (i.e. chewing and swallowing), foods that were solid, high in protein, and slowly chewed helped people feel fuller faster. On the other hand, foods that were liquid or soft, fatty or sweet, and quickly consumed didn’t satisfy people. Fats in particular were least satiating. Sound familiar?

Whole, unprocessed foods that are higher in protein and/or require a lot of chewing – such as lean meats and fibrous vegetables – increase satiety.

Refined, processed foods that are higher in fat and sugar, and have creamy or liquid textures – such as sugary drinks, sweet peanut butter, or ice cream – don’t satisfy us as much. We keep eating these way past the point of our caloric requirements.

In addition, slower eating and smaller bites help release the retronasal aroma compounds. Conscious attention to food’s scents and flavours also helps.

This may be one reason why the French and Italians are leaner than Americans despite higher-fat diets: they simply eat more slowly and consciously. Lunch in France and Italy is a meal that’s slowly savoured, ideally with friends. Portions are smaller, while the flavours and scents of the carefully prepared whole foods are richer. Lunch in the United States is a furtive, hurried affair often done alone while hunched over a car’s dashboard or a computer. Portions are larger, while flavours and scents of the highly processed foods are often appealing but rudimentary. (Compare, for example, a slice of local French artisan cheese with the bland polymer that is “processed American cheese”.)

Not coincidentally, rapid eating is associated with binge behaviour and overeating. Binge eaters chow down at light speed, focused myopically on the process of grasping and pushing food into their mouths, often barely stopping to chew. Even if one isn’t technically binge eating, eating rapidly prevents our natural satiety mechanisms from kicking in.

If we can’t smell what we’re eating, we can’t signal our brain or downstream digestive systems that food is coming. This affects hormone release in our stomachs and intestines, which also affects our feelings of fullness. More on this in Chapter 4.

The take-home message is pretty simple. In order for our ortho- and retro-nasal systems to help us eat well:

Choose whole, unprocessed foods, including high-fibre produce and lean protein

Take small bites

Eat slowly and thoughtfully

Don’t drink your calories

FlavourBoth scent and flavour are simply collections of volatile compounds that we perceive and interpret chemically. Yet that’s like saying love is a series of electrical signals in the brain: it’s technically true, but it doesn’t quite capture it.

When I was a child, I was thoroughly disgusted by my father’s flavour preferences. He loved things that tasted awful to me: wine, coffee, turnips, salted fish – bleah!! He’d crack open a can of sardines and eat it while standing over the kitchen sink as my two sisters and I made gagging sounds.

My theory of aging is that it’s simply a process of becoming the person you used to mock. At age 4, the taste of fish was utterly repellent to me. I tried coffee and spit it out all over the table. At age 14, I tried pickled herring at a Jewish wedding and thought it wasn’t so bad. I could manage coffee if I filled the cup half-full of cream and sugar. At age 34, I too was eating cans of sardines over the sink between swigs of black coffee. Now, in my late 30s, I love all these “yucky” foods my father does.

I’ve long wondered about food’s flavour. Why do some people like certain flavours and not others? Why do our tastes change over time? Where does flavour come from?

In good (or bad) tasteLet’s start by looking at where flavours come from. Like scents, flavours interact dynamically with our chemoreceptors. As we’ve seen, scent and flavour are closely related. In fact, we’ll find a food off-putting if we think the smell and taste are incongruent.

For instance:

Pure vanilla extract isn’t sweet at all. We just normally put vanilla into sweet foods, so we expect things that smell like vanilla to be sweet.

Many new wine tasters are puzzled when they taste a dry fruity wine – again, the fruit scent suggests a sweet-tasting liquid, but the flavour doesn’t match.

Have you ever tried eating a spoonful of dry cinnamon? Bleah!

I once knew a guy who found the concept of fruit and meat together entirely abhorrent. In his mind, fruit should be sweet and meat should be savoury, and that was that. I tried all manner of coaxing: fruit salsas over grilled fish, pork with apples, ham with pineapple, green mango salad with chicken… All were met with revulsion. I eventually had to admit defeat. His taste preferences were simply too rigid to accept the fruit-meat combination.

Also like scents, flavours and textures come from the chemical makeup of the food. Some chemicals, such as sodium ions, work via ion channels. Other chemicals work with G-proteins, particularly one known as gustducin. (There’s those G-proteins again!)

Acids such as acetic acid in vinegar, and ascorbic and citric acid in lemon, produce sour flavours. They may also produce an astringent texture and the “sourpuss effect” (discussed further below).

Bitter flavours come from alkaloids. There is a phenomenon known as “pine nut mouth” that sometimes affects people after eating pine nuts.

Mineral ions, particularly sodium but to a lesser degree, ions such as potassium, produce salty flavours. They may also produce chalky textures.

Sugars such as sucrose, glucose, and fructose produce sweet flavours, as do sugar alcohols such as sorbitol, maltitol, and erythritol.

Protein-based compounds such as glutamate produce savoury, meaty flavours often known as umami.

Sugar and protein together, when heated, produce the characteristic flavours of foods such as browned meat or caramel in a process known as the Maillard reaction.

Sulfur compounds, found in vegetables such as cabbage, broccoli, and Brussels sprouts, produce bitter flavours, which develop strongly if the foods are overcooked or left to sit for a while. They also produce the scent we associate with rotten eggs, as eggs are high in sulfur.

Alkaloids

Terpenes are hydrocarbon structures found in plants (often as volatile oils or alcohols). Examples of terpene-based scents/flavours include:

o citrus (think of orange peels)

o vegetal or earthy (think of carrot peels and green peppers)

o herbal (think of fresh basil or oregano)

o medicinal or minty (think of pine and eucalyptus)

Non terpenoids

Compounds in smoke and coffee formed when carbons are converted ?

Creamy textures usually come from fats

Astrigent textures, which make you feel like you’ve been sucking on a cotton ball, come from tannins. You may have noticed these when tasting very dry wines or black tea that’s been steeped too long. Calcium oxalate, which appears in foods such as spinach and rhubarb, can also create a “chalky mouth” sensation.

Spicy and minty flavours and sensations come from compounds that stimulate the same receptors that sense hot and cold temperature as well as pain. In other words, the chemical makes your brain think you’re touching something hot or cold.

Have you ever wondered why some people prefer sweet foods, while others prefer salty foods –why some people take their coffee black; why some people love bitter greens while others would rather chew on an old pair of underwear than eat Brussels sprouts? Not everyone can perceive these flavours equally. We’ll look at why that is in a bit.

What’s in your mouth? The case of wineFor many people, the idea of wine tasting seems like an exercise in pretentious imagination.

People slug the liquid, slosh it around like mouthwash, and then come up with all kinds of snooty-sounding descriptors like “mineral notes”; “fruit-forward”; “hints of leather and tobacco”; and “oaky”. Movie buffs will remember the satiric scene in the film Sideways where Paul Giamatti’s wine snob character plugs his ears while tasting wine, supposedly to experience the wine better.

Countless adjectives have been harmed in the making of wine descriptions: crisp, floral, bold, ripe, round. Objects and substances that seem to have no relation to grapes are invoked: leather, cedar, citrus, peppers, chocolate, mushrooms.

If you aren’t trained to taste wine, wine will just taste like… wine.

But if you are trained to taste wine, you will taste those flavours.

Yet here’s the puzzle: the flavours aren’t always literally in the wine. A tobacco flavour, or note, doesn’t mean that the vintner accidentally dropped her half-smoked Marlboro in the brew.

So where do wine flavours come from? C’mon, those wine tasters are just making this up, aren’t they?

Well, in fact, the same chemicals that make those flavours in other foods are present in the wine. The chemical composition of the grapes, or the chemicals created when the grapes are processed, determines the flavours.

For example, if you smell or taste apples when you sip a white wine, it’s probably because both apples and grapes contain malic acid. If the wine has a kind of musty, vegetably flavour, like an old green pepper, it probably contains methoxypyrazines – which are also in green peppers. Even the “buttery” flavour of chardonnay actually comes from the same chemical – diacetyl – that’s found in butter. Cool, huh?

The chart below describes some common wine flavours, and where they come from.

If you smell/taste: It might be from:

Vegetables (e.g. green peppers)

methoxypyrazines

Grass, tea, honey, lime or pineapple

norisoprenoids

Apricots or peaches terpenes

Flowers cis-Rose oxide

Eucalyptus or camphor vitispirane

Diesel or kerosene trimethyl-1,2-dihydronaphthalene (TDN)

Coconut, woody or sweet wine lactone

Blackcurrant 4-Mercapto-4-methylpentan-2-one 13 (MMP)

Butter diacetyl

Black pepper rotundone

Sometimes, our memories beat us to the punch. As I’ve mentioned, smell and taste are closely linked to memory. We’ll often feel or imagine a flavour or scent before we can put words to it.

Once, when tasting a wine, I was struck by a sudden memory of my grandmother’s attic, with old clothes stored in a cedar chest. I groped for words to name the flavours, hesitant to insult the woman pouring, but finally settled on an apologetic “musty”.

Luckily it was no faux pas – the earthy note is part of the wine’s unique chemical bouquet. My brain linked the taste to my recollections and then – much more slowly – to language.

Our tastes can be fooled by our eyes and other higher-level prejudices such as our convictions about upscale wines. Winemakers can manipulate people’s perceptions by altering wine’s acidity, astringency and even colour. Consumers given white wine with red food dye in it described red fruit aromas such as cherries and not the flavours that were actually present. And if I slap a $50 price sticker on a bottle I bring over to your house, you’ll probably do your best to pronounce it a “sophisticated bouquet”, even if it’s really $5 plonk.

Keep this in mind the next time you go out for a fancy dinner!

Our saliva’s enzymes depend on our diets – if we eat a diet high in carbohydrates, our saliva will be chock-full of amylase, which breaks those carbs down. Indeed, babies produce almost no amylase until a few months of age, coinciding with when they’re fed cereals.19 Neat, huh?

We’re quite the spit factories – on any given day we produce around a litre of the stuff. Saliva also has antimicrobial properties and immune proteins, which makes it a first line of defense against pathogens such as bacteria, viruses, and fungi.

Fun factoid! Ever notice that intense sensation that you get deep in your cheeks and jaw when you bite into something sour, like a lemon or vinegary pickle? This is from our parotid salivary glands, located just under and in front of our ears, shooting a sudden stream of spit out to respond to the sour taste. Since one of saliva’s jobs is to buffer the acid that can cause cavities, it makes sense that a sour taste – which signifies the presence of acids – would induce a Flashdance-worthy bucket of liquid. Call it the “sourpuss effect”.

Our saliva is actually an important first step in digestion. If we don’t produce enough saliva, we don’t digest things properly.

Remember our G-proteins? The G-protein gustducin is a big player in helping us taste.

Research has shown that TAS2Rs (taste receptors, type 2, also known as T2Rs) such as TAS2R38 coupled to the G protein gustducin are responsible for the human ability to taste bitter substances (wikipedia)

Flavouring agentsFlavourings – what are they? Legal requirements20

Check Codex Alimentarius

Flavouring substances: chemically defined substances with flavouring properties. Defined in IOFI Code of PRactice and EU Flavour Directive 88/388/EEC [1,2]

Natural

Nature-identical

Artificial

Flavouring preparations “natural complexes used b/c of their flavouring properties. They contain flavouring constituents and they are obtained by appropraite physical, microbiological or enzymatic processes from foodstuffs or other material of vegetable or animal origin, either in the raw state or after processing for human consumption by traditional food preparation processes (incl. drying, torrefaction and fermentation)

Process flavourings – products obtained by heating a mix of ingredients to <180C for <15 min. Ingred themselves don’t necessarily flavour. Must contain nitrogen/amino and reducing sugar (Maillard?).

Flavouring adjuvants are substances added to flavourings or their processing in order to “ensure the safety and quality of flavourings and to facilitate the production, storage, and intended use”. May also include flavour modifiers.

What are natural flavourings? Definition varies by region; all defined as natural in EU are so in US; reverse is not true. In US, naturalness of original product defines naturalness of flavouring. EU also includes process, which thus excludes many chemical processes.

Estimated that total flavour and fragrance market is about $12B; flavours about half of this.21

MSG, artificial flavours, sweeteners

Flavour comes from:

1. food properties: all physical, chemical and biological elements of food itself (German 32)

2. “various immediate processes of eating and all the aspects related to the physiology, anatomy and physicochemistry of the oral space.” (32) “entire oral environment”: mouth structure, mode of eating, taste buds, etc. – individual physiological variation

3. perceptive, psychosocial factors – culture, education, mood, age, memories, attention etc. What we expect to smell/taste. (Experience of tasting something that didn’t’ look like it tasted, or smelled fruity but was dry [wine] etc)

Factor 1 empirical; factor 2, 3 subjective and highly individualized.

Food smell – volatile aromatic compounds interact with olfactory epithelium. Carried in air. Aroma important beforehand b/c helps us judge whether to eat something. Once food is in mouth, volatile compounds released into oral cavity, travel thru retronasal passages to throat and nose. Orthonasal and retronasal are different routes/types of aromas. Volatile transport affected by things like heat, air density.

How are common foods made? Compare real vs fake foods (artificial sweeteners, flavours)

Where does feeling of hunger come from?

German et al argue that it relates “primarily to macronutrient and calorie content and not to quality of food, though animals demonstrate nutrient-specific hunger. HUmans feel hunger for energy and apparently do not feel hunger for the essential nutrients except for water – thirst is a special “hunger” for water. B/c energy governs the sensation of hunger, energy determines hunger cues – theory that high energy foods = high energy diets – “caloric overconsumption at the expense of vitamin-rich and mineral-rich diets”.

Rules of eating wellWhen you “feel like eating”, ask yourself, “Why do I feel this?”

Help your sniffers and tasters do their jobs. They benefit and protect you. Learn to smell and taste effectively and intelligently. Be conscious, mindful, and aware. This requires practice.

Be curious with real, unprocessed, whole foods. Try new scents and flavours. Re-acquaint yourself with familiar scents and flavours. Sniff, chew, and slurp foods inquisitively. Roll them around in your mouth to judge texture and note flavour changes.

Be careful with fake food. Recognize that scents and flavours in processed foodlike substances can (deliberately) mislead you.

Understand that scent and flavour help us judge food. As you make food choices, ask yourself what role scent and flavour plays in your decisions. Ask whether you are being fooled or guided.

Treat your smeller and taster as you would a cherished partner. Invest in high quality flavours and scents. Choose smaller portions of better real food over larger portions of crap.

If you’re craving a steak, get a small portion of a wonderful, pasture-raised cut of meat and cook it properly. Don’t opt for a meat-flavoured, industrial-chemical-laced protein puck from the local fast food joint.

If you want cheese, buy a small piece of good artisan cheese and enjoy it slowly. Don’t choose a cheap orange-coloured edible polymer or worse, cheezies.

If you want chocolate, get a few Godiva truffles or good dark chocolate. Don’t buy a big brown block of sugary wax.

Take small bites, and chew things thoroughly. Savour good food’s scents and flavours.

Eat slowly and thoughtfully, without mindless distractions such as watching TV or driving. If you have distractions, make them mindful ones if possible. For example, if you have the pleasant distraction of social interaction, talk about what you’re eating, and be aware of it together.

As much as possible, don’t drink your scents and flavours. If you do drink them, be aware and enjoy it.

If you drink coffee, drink good coffee and don’t drown the taste in sugar and artificial flavours. Sip it mindfully instead of guzzling it while you speed down the highway. When possible, treat coffee tasting like a wine tasting – try different roasts and blends.

Speaking of wine tasting, if you drink wine, visit a winery and learn to taste wine properly – it’s a skill that you can then apply to tasting other foods. Don’t be intimidated; ask questions and find out how the pros do it. If you can’t taste all that stuff they say is in there, don’t worry – just practice observing what scents and flavours you notice in your food and drink.

1 Proust, Marcel. Remembrance of Things Past. Volume 1: Swann's Way: Within a Budding Grove. Orig. pub 1913. French Pleiade edition translated by C.K. Scott Moncrieff and Terence Kilmartin. New York: Vintage, 1941.2 Ketterer, C., et al. “Acute, short-term hyperinsulinemia increases olfactory threshold in healthy subjects.” International Journal of Obesity (23 November 2010) | doi:10.1038/ijo.2010.2513 Cited in Ketterer et al 2010: Julliard AK, Chaput MA, Apelbaum A, Aime P, Mahfouz M,Duchamp-Viret P. Changes in rat olfactory detection performance induced by orexin and leptin mimicking fasting and satiation. Behav Brain Res 2007; 183: 123–129.4 Cited in Ketterer et al 2010: Richardson BE, Vander Woude EA, Sudan R, Thompson JS,Leopold DA. Altered olfactory acuity in the morbidly obese. Obes Surg 2004; 14: 967–969.

Roessner V, Bleich S, Banaschewski T, Rothenberger A. Olfactory deficits in anorexia nervosa. Eur Arch Psychiatry Clin Neurosci 2005; 255: 6–9.5 German, J. Bruce, Chahan Yeritzian, and Vladimir B. Tolstoguzov. “Olfaction: Where Nutrition, Memory, and Immunity Intersect.” In Berger, ed. Flavours and Fragrances. 25-41. (25)6 German, 25.7 The Nobel Assembly at the Karolinska Institute. “The Nobel Prize in Physiology or Medicine 1994 Press Release.” October 10, 1994.8 Ebrahimi, Farah A.W. and Andrew Chess. “Olfactory G Proteins: Simple and Complex Signal Transduction.” Current Biology 8 no.12 (1998): R431-R433.9 Margot, Christian. “A Noseful of Objects.” Nature Neuroscience 12 no.7 (July 2009): 813-814.10 Buchanan, Tony W., Daniel Tranel and Ralph Adolphs. “A Specific Role for the Human Amygdala in Olfactory Memory.” Learning and Memory 10 (2003): 319-325.11 Kennedy DP, Gläscher J, Tyszka JM, Adolphs R. “Personal Space Regulation by the Human Amygdala.” Nature Neuroscience 12 no.10 (October 2009): 1226-1227.12 Zald, David H. and Jose V. Pardo. “Emotion, Olfaction, and the Human Amygdala: Amygdala Activation During Aversive Olfactory Stimulation.” Proceedings of the National Academy of Sciences 94 no.8 (April 15, 1997): 4119-4124.13 Doty, Richard. Handbook of Olfaction and Gustation, 2nd ed. Informa Healthcare; 2003.14 German 29.15 USDA Food Safety and Inspection Service. “Oklahoma Firm Recalls Beef Products Due To Possible E. Coli O157:H7 Contamination.” Recall Release December 24, 2009. FSIS-RC-067-2009.16 Textbook of Dental and Oral Anatomy Physiology and Occlusion17 Ruijschop, Rianne M. A. J., Alexandra E. M. Boelrijk, Cees de Graaf and Margriet S. Westerterp-Plantenga. “Retronasal Aroma Release and Satiation: a Review.” Journal of Agricultural and Food Chemistry 57 no.21 (November 11, 2009): 9888–9894. DOI: 10.1021/jf901445z18 Ketterer, C., et al. “Acute, short-term hyperinsulinemia increases olfactory threshold in healthy subjects.” International Journal of Obesity (23 November 2010) | doi:10.1038/ijo.2010.25119 Ruhl, S. et al. “Proteins in Whole Saliva during the First Year of Infancy.” Journal of Dental Research 84 no.1 (2005):29-34.20 Berger, Ralf G. Flavours and Fragrances: Chemistry, Bioprocessing and Sustainability. New York: Springer; 2007.21 van der Schaft, Peter H. “Chemical Conversions of Natural Precurors.” In Berger, ed. 285-301.