Challenging Beliefs about Flavor

Kevin Liu

February 13, 2012

Neurogastronomy: How the Brain Creates Flavor and Why It Matters – Reviewed.

The preeminent expert in the field lays the foundation for a new brain-based understanding of how we experience food.

When Modernist Cuisine, the Art and Science of Cooking finally came out in early 2011, food geeks around the world rushed to buy it (assuming they had saved up the requisite small fortune). But that enthusiasm soon turned to dismay, even fear, for many of them. It seemed that Modernist Cuisine had succeeded in pondering, unequivocally answering, and even gorgeously photographing every imaginable food and science question in existence. The curious masses had no more need for experiments, hacking consumer goods, or scouring obscure food forums. They needed simply to turn to page 2^25, and lo, their questions would be answered. Was there nothing else in the food world worth exploring?

Enter “neurogastronomy.”

Author Dr. Gordon Shepherd, a neurobiologist by trade, answers few questions in this book. Rather, he elucidates the framework for a whole new set of food questions for his fellow geeks to explore. His language often slips into difficult-to-decipher academic terms and references to specific experiments with only vaguely promising results. But in its own way, Dr. Shepherd’s style can be surprisingly refreshing. Neurogastronomy is not Malcolm Gladwell’s clever and witty if somewhat exaggerated simplification of other people’s work. Both Shepherd’s name and legacy appear on the majority of the research he cites; his expertise is unquestionable. His takeaways are not always easy to find or understand quickly, but they are important enough to merit an extra moment or two of consideration.

The book opens with a staggering claim: whereas the tongue can only sense 5 (maybe 6, max) different tastes, the nose knows literally thousands of different scents. As a result, the majority of what we know as “flavor” actually comes from the nose. Of course, most people think flavor comes from the mouth, but this actually results from a nervous system property known as “referred sensation”

Taste and smell are perceived by completely different parts of the brain. Most people have a rough understanding that the nose plays an important part in flavor perception. But Gordon Shepherd knows a lot more about the topic than most people. For example, our perception of smell is processed by the prefrontal cortex (PFC) portion of the brain – the newest and most complex part of the brain, responsible for language and rational thought. Tastes from the tongue, on the other hand, are processed by the thalamus and the insula, more primitive brain areas that respond more quickly to inputs. These differing pathways help to explain why even babies understand that sweet deserves a smile while bitter begets “icky face,” but a sommelier might spend years training her nose.

I personally keyed in on the fact that the tongue can sense over 100 different shades of bitter. While the tongue experiences the other four tastes only in terms of intensity, it had to evolve a keener perception of bitter agents because bitterness in nature often implies poison. For the modern gastronomic homo sapiens, however, this means that bitterness can add a complexity to foods other basic tastes cannot. Also see my post on bitterness and cocktails.

The section of the book explaining smell receptors sheds some light on the developing field of “flavor pairing.” Flavor compounds are all organic compounds varying in length and constituent parts. Smaller, lighter molecules more easily escape into the air when food is chewed, so they are more likely to be sensed by the nose as we breathe out (this is called retronasal smell). Our noses are lined with thousands of olfactory receptors that each respond to a broad spectrum of scents. Every imaginable scent triggers a different subset of these receptors; a sort of “smell image” is created in the brain as a result. Most interestingly, our smell images can be amplified or even transformed when certain flavors are experienced together – when they are paired.

A recent academic investigation of flavor pairing revealed that western palettes prefer flavor compounds that match each other, while Asian cultures tended to avoid consonant tastes. But are these preferences learned? Are the genes responsible for olfactory receptors somehow different between races? Is there a certain type of flavor contrast Asians prefer that creates particularly sharp smell images?

Shepherd himself uses the latter fourth of Neurogastronomy to pose his own questions about food and the brain. Is an overload of pleasurable flavor compounds in modern foods responsible for widespread obesity? How much of flavor perception is conscious versus unconscious? Eating ties directly into the reward and punishment centers of the brain, areas that handle much of our decision-making. How does flavor affect the food we choose? What about other decisions? Like the trained scientist he is, Shepherd declines to conclusively answer any of these questions outright. Instead, he conservatively asserts that ongoing research holds promise.

The book Neurogastronomy might not be able to answer any of these questions outright, but the field it precedes will likely get to them in due course. In the meantime, serious food geeks (like you, I hope) should definitely get this book to foster curiosity and experimentation. Everyone else can wait for Gladwell’s summary.

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