In this blog, we're diving back into one of my favorite topics related to truffles: human sensing and perception, specifically our amazing sense of smell. This post is part of our series on the science of food pairing and neurogastronomy (check out the links below). In this deeper dive, we'll explore what makes our sense of smell so special compared to other animals, and in particular how human and dog noses differ.
Smell, of course, plays a huge role in enjoying truffles and food. But for a long time, this sense has been underrated. Even Aristotle once said, "our sense of smell is inferior to that of all other living creatures, and also inferior to all the other senses we possess." But when you think about it, smell has shaped human history, a topic we'll dive into below. To really get to know how amazing our sense of smell is and its role in our species’ development, we'll compare it to the ultimate sniffing machine: the dog. We will then look at the action of our smell machine and the main factor that sets us apart from all other animals, the role retronasal smell plays in detecting the flavours of the food we eat.
What is retronasal smell? And why is it important. Well for we truffles lovers, don’t forget the main action of truffle and therefore the impact on our senses is via their aroma, so knowing how your smell system works will allow you to get the best out of your truffle experience. But before we get too deeply into that, let’s take a closer look at how smell has shaped the course of human history.
But wait, before we go too far, I want to acknowledge that this post draws heavily on the work of Gordon M. Shepherd and his book Neurogastronomy which is an amazing read. You can get a copy of it here.
The role smell and flavour have played in human history.
In our school history lessons, we often learn about the pivotal role spices played in shaping global trade. However, this narrative didn't begin with Marco Polo's journey to China. Over a millennium earlier, the Romans had already established extensive trade routes reaching as far as China and the South Pacific. They introduced Europe to an array of captivating flavours and aromas, enriching culinary experiences across the continent.
Contrary to popular belief, Christopher Columbus' expedition wasn't solely about proving the Earth's roundness; its primary objective was to discover a more efficient route to the sources of spices. Furthermore, the exploration and exploitation of the Americas during the sixteenth and seventeenth centuries weren't solely driven by the quest for gold; they were also strategic moves to dominate the spice trade and production.
It has been argued that the major sea lanes established by the British in the eighteenth and nineteenth centuries for shipping tea and spices from Indonesia played a crucial role in building their empire. These routes paved the way for the rise of world powers and their economies in the nineteenth and twentieth centuries. Today, we have inherited and adapted these routes, shifting from controlling the trade of tea and spices to overseeing the sources of oil and a variety of other goods, thereby facilitating the spread of global capitalism.
‘Erick Schlosser in Fast Food Nation: The dark side of the All-American Meal, was very clear about how ‘the human craving for flavour has been a largely under-acknowledged and an under-examined force in history. Royal empires have been built, unexplored lands have been traversed, great religions and philosophies have been forever changed by the spice trade. In 1492 Columbus set sail to find seasoning. Today the influence of flavour in the world market is no less decisive. The rise and fall of corporate empires of soft drink companies, snack food companies, and fast-food chains is frequently determined by how their products taste.’
The value we humans place on our sense of smell and appreciation of flavour has been vastly underappreciated in terms of its influence on history and, perhaps even more importantly, our economic progress as a species. Consequently, science has only recently begun to focus on our remarkable sense of smell and its impact on our lives. Until now, scientists have had a very rudimentary understanding of how the brain constructs neural representations of the small molecules that transmit odour. Often, subtle chemical changes — a few carbon atoms here or oxygen atoms there — can lead to significant differences in smell perception. But why does this happen? You can explore some of the latest research here if you're interested. For now, let's look at how human smell has evolved by comparing it to our trusty friend, the dog's nose.
Dogs, humans and retronasal smell
Retronasal smell is the olfactory mechanism that allows humans to better detect the flavours of our foods, while dogs, who need to detect what is in their environment, have noses better adapted for orthonasal smell. What is the difference between these two types of smell, and how do they work? To best understand the advantages and implications of each, let's start by comparing them, beginning with the dog's nose.
Have you ever really noticed the shape of your dog's nose? It's an engineering masterpiece designed to turbocharge their ability to smell the world around them. The science of fluid dynamics—the study of how air and water pass over and through objects like airplane wings and tubes—has been used to shed light on the remarkable power of a dog's nose.
Breathing in to sample scents in the air by sniffing is the primary design feature of a dog's nose. This orthonasal smelling process begins at the dog's nostrils, known as nares. If you look closely, you'll notice the shape of your dog's nares, which feature a round opening encircled by membranes called alar folds, and a curved slit to the side, resembling a comma lying on its side. When a dog sniffs, it draws air in through the central opening, using muscles in the alar folds to enlarge the opening. When it breathes out, it contracts different muscles to force air out through the side slits. The main advantage of this mechanism is to ensure that exhaled air does not interfere with the odorized air being inhaled. This is particularly important when dogs are tracking scents close to the ground.
When dogs are sensing an odour in the air, typically with low concentrations of odour molecules, they slow their sniffing rate to take longer inspirations with their mouths open, drawing air over the olfactory membranes inside the nose slowly for careful detection. For detecting odours on the ground, dogs decrease the reach of their noses (the distance around the nose from which they draw air, usually 10-15 cm with their heads up) by placing their noses as close to the ground as possible. This makes the lines of airflow denser, enhancing the concentration of inspired odour molecules, such as those of truffles.
Another notable design feature of a dog's nares is their placement on its body. Positioned at the same level as the hips, a dog's nose is optimally situated to sniff odours both on the ground and in the air. This head position also facilitates social interactions. Dogs greet each other with a sniff of the mouth to get an idea of what the other has eaten, and their head position also allows them to detect what their new friend had for dinner last night and assess their sexual availability.
The dog’s snout
In the snout, the olfactory sensors are located at the back of the nasal cavity near the brain, lining a series of bony convolutions to increase the surface area of the sensory sheet. Between the nostrils and the receptors is an array of convoluted cartilage covered by a respiratory membrane. These convoluted cartilage tubes serve three important purposes to improve smell: they warm the air, they moisturize it, and they clean it. Just as muscles around the nostrils can direct air, muscles within the nostrils also direct air along the most appropriate tube for each breath. Additionally, a dog can increase its rate of respiration to six to eight times per second, which significantly enhances its ability to detect scents. Now that's turbocharged smelling—how many can you do?
In contrast to these orthonasal (sniffing) optimizations, the pathway for retronasal smell—from the back of the mouth through the nasopharynx to the nasal cavity—is long and relatively narrow (see pictures above). Clearly, compared to humans, dogs are preferentially adapted to orthonasal smell. Now, let's look at human smell.
Evolution of the human nose
Theories of how things evolved are, at best, highly speculative. However, for the neurogastronomic scientist, the answer is clear. Because of what we know about the importance of our relationship with food, evolution seems to have advantaged us by enhancing our appreciation of it through retronasal smell. While there may be some truth to theories about the snout’s reduction enabling the eyes to move together for stereo vision or a decreased need to process roughage-rich food reducing the need for a large mandible, the real benefit lies in how these changes reduced the distance between the nose and olfactory sensors. This also shortened the nasopharynx, improving retronasal smell. This shortening of the nasopharynx is particularly important as it allows odours released from food in the mouth to reach the smell receptors in the nasal cavity more effectively.
There are several compelling reasons why retronasal smell may have held particular significance for humans. Firstly, as we migrated out of Africa and began to explore new territories, retronasal smell likely played a crucial role in our ability to discern and appreciate the diverse flavours of the foods we encountered. Secondly, the discovery of fire approximately 400,000 years ago revolutionized our culinary landscape, imparting richer tastes and aromas to our food. Retronasal smell would have heightened our enjoyment of these newfound flavours. Lastly, the advent of fermentation, allowing for the preservation and transformation of foods and liquids, opened a plethora of new flavours and aromas for us to savor. The fermentation process intensified taste, smell, and flavours, further enriching our sensory experiences.
Humans as super smellers
Recent research on human smell has unveiled capabilities that far surpass the traditional view. Contrary to the notion of having a weak sense of smell, it appears to be remarkably powerful, prompting some scientists to propose that humans and their primate relatives are in fact the 'super smellers' of the animal kingdom.
Our unique ability to deeply appreciate the flavours of the food we consume has undeniably influenced our history, evolution, and our role in shaping the earth, notably through endeavors like agriculture. Is it any wonder, then, that our heightened sense of smell has led us to become so captivated by the allure of the truffle?
Well that's a wrap. A post about smell, its development and how it lead us inevitably to the truffle. If you liked this post, please consider sharing the joy with your friends and fellow truffle lovers. If you've got any truffle stories or questions, as always, we're all ears.
Ciao for now truffle lovers.
Carmine
Commenti