Mouthfeel: How Texture Makes Taste
By Ole G. Mouritsen and Klavs Styrbæk
()
About this ebook
Collaborating in the laboratory and the kitchen, Ole G. Mouritsen and Klavs Styrbæk investigate the multiple ways in which food texture influences taste. Combining scientific analysis with creative intuition and a sophisticated knowledge of food preparation, they write a one-of-a-kind book for food lovers and food science scholars. By mapping the mechanics of mouthfeel, Mouritsen and Styrbæk advance a greater awareness of its link to our culinary preferences. Gaining insight into the textural properties of raw vegetables, puffed rice, bouillon, or ice cream can help us make healthier and more sustainable food choices. Through mouthfeel, we can recreate the physical feelings of foods we love with other ingredients or learn to latch onto smarter food options. Mastering texture also leads to more adventurous gastronomic experiments in the kitchen, allowing us to reach even greater heights of taste sensation.
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Mouthfeel - Ole G. Mouritsen
MOUTHFEEL
Arts and Traditions of the Table: Perspectives on Culinary History
MOUTHFEEL
How Texture Makes Taste
Ole G. Mouritsen and Klavs Styrbæk
TRANSLATED AND ADAPTED BY MARIELA JOHANSEN
Columbia University Press New York
Columbia University Press wishes to express its appreciation for assistance given by the Danish Arts Foundation toward the cost of publishing this book.
Columbia University Press
Publishers Since 1893
New York Chichester, West Sussex
cup.columbia.edu
Copyright © 2017 Columbia University Press
All rights reserved
E-ISBN 978-0-23154-324-8
Library of Congress Cataloging-in-Publication Data
Names: Mouritsen, Ole G., author. | Styrbæk, Klavs, author.
Title: Mouthfeel : how texture makes taste / Ole G. Mouritsen and Klavs Styrbæk; translated and adapted by Mariela Johansen.
Other titles: Fornemmelse for smag. English | Mouth feel
Description: New York : Columbia University Press, 2017. | Series: Arts and traditions of the table : perspectives on culinary history | Translation of: Fornemmelse for smag. | Includes bibliographical references and index.
Identifiers: LCCN 2016032426 (print) | LCCN 2016032605 (ebook) | ISBN 9780231180764 (cloth : alk. paper) | ISBN 9780231543248 (e-book)
Subjects: LCSH: Food texture. | Taste. | Food—Sensory evaluation. | Food preferences. | Cooking. | LCGFT: Cookbooks.
Classification: LCC TX546 .M6913 2017 (print) | LCC TX546 (ebook) | DDC 664/.072—dc23
LC record available at https://lccn.loc.gov/2016032426
A Columbia University Press E-book.
CUP would be pleased to hear about your reading experience with this e-book at cup-ebook@columbia.edu.
COVER IMAGES: © iStock and Shutterstock, additional photos by Jonas Drotner Mouritsen
COVER DESIGN: Milenda Nan Ok Lee
CONTENTS
Preface
Acknowledgments
1 The Complex Universe of Taste and Flavor
The Mouth and the Nose: Where It All Begins
Mouthfeel: A Central Element of the Total Flavor Experience
Astringency and Kokumi: Not Exactly Mouthfeel, but Something Like It
Sensory Confusion
The Interplay Between Mouthfeel and Other Sensory Impressions
Neurogastronomy: Flavor Is All in the Brain
2 What Makes Up Our Food?
Food from the Tree of Life
Edible Molecules
Biological Soft Materials
Water: Both Stable and Versatile
Processed Food
Synthetic Food: Note-by-Note Cuisine
3 The Physical Properties of Food: Form, Structure, and Texture
Structure and Texture
Foods as Solids, Liquids, and Gases
More Complex States
When Food Changes Form, Structure, and Texture
4 Texture and Mouthfeel
When We Chew, We Are Using the Taste Muscles
What Is Texture?
How to Describe Texture
Changing Texture
5 Playing Around with Mouthfeel
Transforming Raw Ingredients
Heat and Temperature
Texture in a Bottle or a Can
Starch: A Very Particular Kind of Thickener
Emulsions and Emulsifiers
Gels and Gelation
Gums
The Effect of Enzymes on Texture
Sugars in Food
Fats in Food
The Surprisingly Diverse Textures of Milk
Amazing Eggs
Glassy, Glossy Foods
Particles in Food
Bubbles in Food
From Soft to Hard and Back Again
6 Making Further Inroads into the Universe of Texture
Legumes, Soybeans, and Sprouts
Vegetables with a Bit of Bite
Grains and Seeds with a Multitude of Textures
The Secrets of Sauces
The Mouthfeel of Soups
Transforming Chewy Dough into Crisp Bread
Crispy Skin and Crunchy Bones
The Texture of Perishability
A Taste Challenge: Some Special Seafood
Frozen Desserts: From Granular and Creamy to Chewy
Texture That Releases Big Bursts of Taste
7 Why Do We Like the Food That We Do?
Enjoyment and Hedonism
Food and Taste Adventurousness
Texture, the Choice of Foods, and Tolerance for Texture
The Perfect Meal
Epilogue: Mouthfeel and a Taste for Life
Glossary
Bibliography
Illustration Credits
Index
RECIPES
Extra-Dry Champignons, Endive, and Umami Crème with Grated, Smoked, and Frozen Egg Yolks and Roquefort
Grilled Beef Heart
Apple Fudge
Crisp French Fries, Peel and All
Six Types of Jelly with Vegetables, Fruit, and Water
Laminar Coffee Shots with Celeriac
Entrecôte de Boeuf
Slow-Cooked Sous Vide Beef Brisket
Really Crisp Old-Fashioned Crullers
Amy’s Apple Pie
Cultured Butter
Instant Churned Butter
Parmesan-Flavored Smoked Cheese with Dried Radishes
Peppery, Chewy, Chocolaty Caramel
Caramelized Potatoes
Candied Seaweed
Old-Fashioned Crispy Spice Cookies
Crisp-Fried Bull Testicle with Sprouts and Parsnip Emulsion
An Experiment: Two Types of Ketchup
Pesto
Sago Soup with Raisins
Arctic Textures
Kidney Bean and Crisp Vegetable Salad
Duck Tongues with Beans and Artichokes
Succulent Daikon
Vegetables, Prepared So That Children Love Them
Kohlrabi Tsukemono
Japanese Cucumber Salad
Muesli with a Difference
Crisp Risotto Balls with Mushrooms, Broad Beans, and Mussel Powder
Ceviche with Chile Peppers and Popcorn, Sprinkled with Nutritional Yeast
Seriously Old-Fashioned Sourdough Bread with a Crisp Crust
Pretzels
Tarte Flambée with Chorizo and Onions
Croutons
Morimoto’s 22-Step Recipe for Perfect Duck Breast
Crisp Pig-Tail Confit
Grilled Cod-Skin Snacks
Dried, Crisp Eel Skin
Snack Made from Cod Air Bladder
Crisp Sprats
Crunchy Skate Wing
Grilled Skate Wing with Swiss Chard
Aged Pork Loin Roast with Asparagus and Béarnaise in Parts
Fish Soup with Fried Squid and Sautéed Starfish Roe
Dehydration of Jellyfish
Jellyfish Salad with Seaweed, Kohlrabi, Horseradish Juice, and Black Garlic
Jellyfish Popsicles
: Where Licorice Meets the Sea
Ice Cream with Sugar-Cured Dulse
Chewy Almond-Milk Ice Cream
PREFACE
Why does eating a piece of chocolate that literally melts on the tongue give us such feelings of decadent pleasure? Why does a freshly prepared hot dog taste very different from one that has taken a trip through the blender? Why do most people prefer their eggs with bacon that is fried until it is crisp? And why is soda pop that has lost its fizz or beer that has gone flat so unappealing? These and many other questions about the sensory perceptions of taste—especially the extent to which they are affected by how food feels in the mouth—piqued our curiosity and were the driving force that led us, a researcher and an experienced chef, to look beyond the chemical composition of a foodstuff and to think seriously about the physical impression it makes. We tackled the problem as a collaborative effort, using the kitchen as the laboratory in which we combined scientific critical thinking with creative intuition and in-depth knowledge about food preparation.
Taste is one of our most important senses. We depend on it to steer us away from ingredients that might be harmful or even poisonous and to guide us toward those that are palatable and nourishing. Here we may think that we are relying primarily on the five basic tastes—sour, sweet, salty, bitter, and umami—which we can describe quite easily. But we have considerably more difficulty in articulating, let alone remembering, the overall sensory impression made by a dish or a whole meal. This is partly because the interplay between taste and smell complicates matters. So does the presence of certain substances in food that are not true taste substances, but react with saliva and the mucous membranes. For example, tannins in red wine can induce a feeling of dryness in the mouth or capsaicin in chile peppers may be irritating or even cause pain. And what we often fail to grasp is the role played by the physical characteristics of what we put into our mouth and how we react to them. Even though this often happens quite subconsciously, it turns out that our liking a foodstuff or rejecting it is often more dependent on how it feels in our mouth, rather than on how it tastes or smells. This sensation is called mouthfeel and it relates to the texture of the food.
Without a doubt, a poor understanding of how taste works and the role of mouthfeel, especially when coupled with a lack of culinary skills, are contributing factors in our tendency to eat portions that are too big and too fattening. At the same time we are adding to our foods increasingly large amounts of sugar, salt, and fats—all of which have been linked to major dietary-related diseases that have taken on epidemic proportions in the past century. Taste is closely linked to appetite, digestion, and feelings of satiety, all of which lead to a natural regulation of food intake. Paradoxically this relates to two opposite effects: many otherwise healthy people have a poor diet and eat too much because the food is unpalatable and not naturally filling; and many who are sick and elderly eat too little because appetite falls off when the food is not tasty. This is a striking reminder of the important contribution that tasty food makes to what we think of as the good life.
It is thought-provoking that, on the one hand, items sold in supermarkets rarely carry any description of the taste or texture that goes beyond a reference to spiciness. On the other hand, the products are usually labeled with precise details about their places of origin, nutritional contents, calorie count, and so on, often supplied to comply with government regulations. And in many cases, taste impressions are derived from fast foods, snacks, soda pop, and candy, all of which have an impact on our health. We would like to see that changed and hope that this volume will help to promote the use of a more precise vocabulary for describing the taste of food, especially texture or mouthfeel.
The answers concerning why mouthfeel is so intimately linked to a healthy diet lead immediately to a host of new questions about what one needs to do to prepare raw ingredients and produce dishes that enhance this aspect of our daily food intake. How does one best thicken a soup or a sauce? How does one produce a crisp crackling on a pork roast? What is the secret of homemade mayonnaise? And how does one prepare vegetables so that they are cooked to perfection? In this book we have tried to provide answers to these and many other questions. We have designed it with several goals in mind: to give an overview of how mouthfeel fits into the perception of taste; to provide a popular introduction to the science underlying taste, mouthfeel, and texture, as well as a systematic review of the properties of raw ingredients that are fundamental to an appreciation of their structure, and with it, their mouthfeel; and to demonstrate the many ways in which mouthfeel can be altered. An extensive glossary and a detailed index are included as a quick reference for those who are not ready to delve too deeply into the science. Nevertheless, we hope that our search for a deeper scientific understanding will serve as a source of inspiration for experienced chefs, nutrition and wellness professionals, food entrepreneurs, and food enthusiasts so that they might join us in our goal of improving food culture as we experience it on a daily basis.
The quest to satisfy our curiosity about mouthfeel has taken us far beyond our own kitchens and laboratories on journeys around the world to places where its central role is well established. We are delighted to be able to share our adventures and experiences in tracking down taste and mouthfeel in their many forms and describe what happens to raw ingredients when we work with them to create softness, crispness, creaminess, elasticity, viscosity, and other textures. Using examples and recipes ranging from the basic to the exotic, we will show how you, the reader, can become adept at navigating through the universe of taste and gain a greater appreciation of its physical dimension: mouthfeel.
ACKNOWLEDGMENTS
The authors wish to thank the following:
Our many colleagues in the multidisciplinary project Taste for Life,
which is supported by the Nordea Foundation, for their inspiration and for opening our eyes and senses to the many facets of the universe of taste: Per Lyngs Hansen for many insightful conversations and discussions about food and science; Mathias Porsmose Clausen, Jinsoo Yi, and Morten Christensen for microscopic examinations of a variety of foodstuffs and for discussions about, and interpretation of, the microcosmos of food—Morten also as well for illustrations and information about milk and milk products; Per Møller and Michael Bom Frøst for conversations and information about sensory science; Kasper Styrbæk and Per Lyngs Hansen for a description of their new method for the calcification of tomatoes; Karen Wistoft for inspirational conversations about taste and the food preferences of children; Mikael Schneider and his four girls, Mille, Tilde, Sally, and Vigga, for demonstrating the jelly bean test and for taking photographs of it; Kasper Styrbæk for his tremendous and creative collaborative work in STYRBÆKS’s kitchen, and Christopher Huus and Zenia Lærke Larsen for their participation in the photo sessions.
Gordon M. Shepherd for information about the interaction between mouthfeel and umami, and his book Neurogastronomy: How the Brain Creates Flavor and Why It Matters has been a major source of inspiration; Jens Risbo for information about cold sweeteners; Amy Rowat for information about the gastrophysics of pies and chocolate and for her recipe for the perfect apple pie; Morihiro Onodera, Tamaki Farms, for information about the perfect sushi rice and permission to use his photographs.
Julie Drotner Mouritsen for enlightenment about psychological concepts and topics; Inger Marie Mouritsen for recipes for old-fashioned crullers and old-fashioned crispy spice cookies; Atsushi Kono from Restaurant Torishin in New York for information about and instruction in preparing tori-yaki; Jeppe Ejvind Nielsen from Restaurant Ulo at Hotel Arctic in Ilulissat, Greenland, for conversations about mouthfeel in Greenlandic food and for making available the recipe for an iced dessert; Koji Shimomura from Restaurant Édition Koji Shimomura, Tokyo, for the picture of the dish with poached oysters in a seawater gel; Daniel Burns and Florent Ladeyn for the recipe for candied winged kelp, which was elaborated at the workshop Arctic Must! in Ilulissat in northern Greenland in January 2014; Liz Roth-Johnson for materials about gelation with starch; Josh Evans and Roberto Flore at the Nordic Food Lab for the recipe for Peas ‘n’ Bees; Anita Dietz for a recipe for seaweed pesto and accompanying photograph; Jens Møller Products for permission to reproduce pictures of Cavi-art products; Alexandre Ponomarenko and Emmanuel Virot for permission to use their pictures of how popcorn develops; Jinsoo Yi for bringing dried jellyfish from Korea; Peter Bondo Christensen for an underwater picture of seaweed; Thormar Thorbergsson, Odense Chokoladehus, for a contribution of chocolate; Kent Stenvang, Egehøj Champignon, for supplying mushrooms and giving a tour of the facilities; Palsgaard A/S for access to the firm’s picture collection and permission to reproduce pictures; Steen Aalund, Løgismose, for supplying molds for special smoked fresh cheeses; Poul Rasmussen for exceptionally speedy delivery of everything good from the sea, including starfish; Kristoff Styrbæk for photographs and engaged conversations about photography.
Jonas Drotner Mouritsen for photography, illustrations, and collaboration on integrating text and graphical design. Joaquim Marquès Nielsen for technical illustrations.
This book was originally written and published in Danish, the mother tongue of the authors. This edition is a fully updated and revised version of the Danish work, translated into English and adapted for a wider audience by Mariela Johansen. Mariela enthusiastically undertook the ambitious task of turning the multidisciplinary material into a coherent, scientifically sound, and very readable book. She did an admirable job not only in translating the text, but also of checking facts, ensuring consistency, and suggesting new material and valuable revisions. The authors are extremely appreciative of her devoted work on this project. We would also like to thank our editor, Jennifer Crewe, for her enthusiastic interest in the project, and Columbia University Press for professional and expeditious handling of the manuscript.
Last, but not least, we wish to thank our families, especially Pia and Kirsten, who have had to live with us as we undertook our journey through the universe of mouthfeel in the course of a couple of years. They have had to lend us their ears and palates on numerous occasions. Thank you for your constant support and love.
The universe of taste and flavor is marvelously complex, not only in terms of the senses involved but also in relation to the words we use to describe it. We often use the words taste
and flavor
rather loosely and interchangeably, without giving too much thought to their precise meaning. We might say that a piece of Brie tastes creamy or that olive oil is light in flavor. While we probably understand intuitively the meaning of these statements, they are inaccurate descriptions of the sensory impressions evoked by these foods. So, as we set out to explore this universe, we are immediately faced with the need to define the concepts of taste and flavor more rigorously.
On the one hand, strictly and scientifically speaking, taste refers only to the recognition of taste substances by the taste buds. On the other hand, flavor is multimodal and engages, to a greater or lesser degree, all five senses. Taste, smell, and touch are all central elements of a flavor impression, while sight, sound, and chemical reactions in the mouth are involved as well. Information derived from all these sources is integrated in the brain to leave us with a single impression of a food or a drink. Later in the chapter we will have a more detailed look at how the process works.
We have all experienced the extent to which taste and smell enhance and interact with each other. The role of the other main aspect of flavor, which is based on tactile sensations and known as mouthfeel, is often overlooked. In this book we have singled it out so as to foster a deeper understanding of how it affects our enjoyment of food and how we can make use of it to prepare more nutritious and flavorful food. Before plunging into how this is put into culinary practice, however, it is useful first to take the time to learn about the scientific underpinnings of flavor science.
The Mouth and the Nose: Where It All Begins
Virtually everything that we need to sustain normal life enters us through our mouth or nose, the main gateways between the material world and the inside of our body: food and drink through the mouth; air, a host of different airborne particles, and odor substances through the nose. These portals are designed to maximize the entry of those substances that are beneficial to us and minimize the possibility of swallowing or inhaling something that is potentially harmful.
The environment in which we live is far from benign; we are surrounded by vast quantities of artificial and naturally occurring substances and microorganisms that can be life-threatening. That is why we are well protected on the outside by a layer of skin, the stratum corneum, which is very dense and difficult to penetrate.
The internal surfaces of our body—that is, those of the oral and nasal cavities, air passages, and the digestive system—are more vulnerable. These areas are covered by mucous membranes, made up of epithelial cells, which form a good barrier against certain substances but allow others to pass through. They perform this function, for example, in the lungs, where oxygen and carbon dioxide are exchanged, and in the intestines, where nutrients are absorbed from the food. Unfortunately, harmful substances, such as poisons, noxious gases, and bacterial and plant toxins, are also able to pass through the mucous membranes and enter the bloodstream and reach the inner organs.
This is why the main gateways, the mouth and the nose, are well guarded by a large number of sensors. In the course of human evolution, these have developed to help us select substances that we need and allow them to pass through while at the same time keeping out those substances that are potentially dangerous and poisonous. These sensors transmit signals about taste, smell, and mouthfeel to the brain, where it is integrated with visual and auditory input and information about chemical reactions in the mouth and nose. This overall sensory impression is what determines whether we will allow something to pass through to the more easily damaged inside of our body. Mouthfeel is an important part of this determination.
Flavor impressions are surprisingly complicated and multidimensional. They are driven principally by the recognition of taste substances by the taste buds, the sensing of aromatic substances in the nose, the way the food feels in the mouth, and chemical effects on the mucous membranes (chemesthesis).
All these different senses are rooted in our nervous system. Like the motor system, this sensory system is connected to either the brain or the brainstem. This happens with the help of twelve paired cranial nerves and of nervelike connections called ganglia. They are either sensory, sending impressions from the senses to the brain, or motor, transmitting signals from the brain to the muscles and organs.
AN EXPERIMENT: THE JELLY BEAN TEST
We all know that food tastes different when we have a blocked nose because of a cold. Actually, its taste is no different, but our sense of smell is temporarily diminished.
You do not need to have a cold, however, to experience the extent to which smell plays a role in flavor impressions. Just pinch your nose closed with your fingers, take a piece of candy—a wine gum, a jelly bean, or a candy with a fruit, cinnamon, or anise flavor—pop it into your mouth, and chew on it without exhaling. You taste only sweetness derived from the sugar or other sweetener in it. Let go of your nose, breathe out, and prepare yourself for a surprise. The candy suddenly seems to taste totally different because the aromatic substances that were added to it are now making their way from the mouth, up into the nose, and sending additional signals to the brain.
Several of the twelve pairs of cranial nerves are involved in identifying taste and odor substances and evaluating the impression made by food. All components of flavor make use of the cranial nerves to communicate with the brain, and this takes place at a very high level, which tells us that all aspects of flavor are important for our survival. The olfactory nerves are the first of these twelve pairs, the optic nerves are the second, and the trigeminal nerves are the fifth. All three are intimately involved with flavor impressions. The sense of smell is directly connected to the brain, the most crucial part of our central nervous system, at the highest cognitive level. Sensations of taste and mouthfeel pass indirectly to the brain through the brainstem, which is where other vital autonomic functions, such as heartbeat and breathing, are controlled.
• Smell is the most discriminating and most important aspect of flavor. The sense of smell is, in fact, much more discriminating than the sense of taste. It is stimulated by airborne substances in one of two ways. Odors are given off by food before it is put in the mouth and are inhaled directly through the nostrils; this is the orthonasal pathway. When we chew on food, aromas are released in the oral cavity and make their way up into the nasopharynx; this is known as the retronasal pathway. Retronasal detection of smell is the most important and well-developed route in humans, whereas dogs, to use a familiar example, detect most scents orthonasally. In both cases, the odor compounds arrive at the top of the nasal cavity, where they are detected by hundreds of discrete olfactory receptors. This in turn propagates an electrical impulse through the first pair of cranial nerves directly to the olfactory center in the brain (the olfactory bulb and the orbifrontal cortex, a region of the frontal lobe). A smaller portion of the signal is transmitted to the limbic system (paleomammalian brain), which is the locus in the brain for memory, feelings, and decision making about rewards and punishments. The sense of smell has a long evolutionary history, with about one out of every fifty genes in the human genome devoted to it. It is vital to our survival and is strongly linked to the subconscious. As a given smell can activate many odor receptors, humans are able to detect the differences between an enormous number of individual smells, possibly as many as 1 trillion. Recent research has shown that humans conceptualize smells as spatial patterns in the olfactory bulb, much in the same way as sight does on the visual cortex, forming a smell image. Nevertheless, our sense of smell is much less sensitive than that in some other species, for example, in bears, because our olfactory receptor neurons are not packed together as densely. But the area of the brain where we process signals from the nose is much larger and more sophisticated. For this reason our sense of smell may actually be much better developed than previously thought. The smell image in the brain of a particular odor can possibly be compared with the visual picture of a familiar face. This can help explain why odors and memories are linked in our mind.
Odor, smell, or aroma?
The words smell,
odor,
and aroma
can be used to denote that which we perceive through the olfactory system. Smell
is used most broadly, particularly in reference to the sense. Although the words smell
and odor
are value neutral, both have acquired a somewhat negative connotation, possibly due to their frequent association with the adjective bad
and its synonyms. An aroma is also a smell, but this word is often used to describe one that is pleasant, such as that of freshly baked bread or a hearty stew.
• Taste, in the sense of what we taste directly on the tongue and in the oral cavity, is a physico-chemical and physiological entity that is localized especially in the almost 9,000 taste buds found on the tongue. The taste substances need to be dissolved in saliva before they enter through the pores of the taste buds to be picked up by the numerous taste cells. Taste cells are a specialized type of nerve cell that are tightly packed in the taste buds like the individual cloves in a bulb of garlic. The various receptors that are sensitive to the five basic tastes—sour, sweet, salty, bitter, and umami—are located in the cell membranes of these nerve cells. When the taste substances are recognized by and bound to the receptors, an electric signal is released via a series of biochemical processes, sent to the brainstem, and from there continues on to the brain. Each taste cell is primarily responsible for one type of basic taste. The various cells that are sensitive to the same basic taste send an integrated signal along a nerve fiber via three separate cranial nerves (the seventh, the ninth, and the tenth) through the thalamus to the taste center in the brain (anterior insula and the frontal operculum). In contrast to the sense of smell, it is not yet known whether the sense of taste forms a taste image on the cerebral cortex in the same manner as the senses of smell and sight.
• Mouthfeel, which will be described in greater detail later in this chapter, is a part of what is known as the somatosensory system. This system is found not only in the mouth, but everywhere in the body—for example, in the skeletal muscles, joints, inner organs, and cardiovascular system. Physical stimuli, including pain, temperature, and tactile sensations, such as pressure, touch, stretching, and vibrations, are picked up by the somatosensory system. It is also affected by the ability to sense the position and movements of the body and parts of the body (kinesthesia). This is linked to mouthfeel through the motions of the tongue as it explores and identifies the size, shape, and texture of a piece of food while chewing on it. Nerve endings in the teeth provide additional information about the structure of the food—its hardness, whether it is crunchy or elastic, and the size of its particles. Like the sensory impressions of taste, nerve signals regarding mouthfeel go indirectly through the brainstem to the brain—that is, to the thalamus and from there to the somatosensory center.
Irritants
Irritants are substances—for example, capsaicin, isothiocyanate, and piperine—that have an irritating effect on the trigeminal nerve (chemesthesis). They are found in many raw ingredients, including onions, chile peppers, black pepper, mustard, wasabi, horseradish, ginger, cress, arugula, and radishes.
• Chemesthesis describes the sensitivity of the skin and mucous membranes to chemically induced reactions that cause irritation or pain and that may damage cells and tissues. In the mouth this is registered as a sharp taste when we eat chile peppers, which contain capsaicin; black peppercorns, which contain piperine; or horseradish and mustard, which contain isothiocyanate. As the endings of the trigeminal nerves (the fifth paired cranial nerves) are the ones affected, chemesthesis is sometimes referred to as the trigeminal sense. Sensations of temperature are related to chemesthesis, in that certain chemical substances can interact with, and in a way deceive, some of the temperature- and pain-sensitive nerves relating to mouthfeel. This gives rise to false perceptions of heat and cold that are not directly related to the actual temperature of the food. Capsaicin induces a burning sensation, whereas menthol, peppermint, and camphor feel cold in the mouth.
The placement of the five sensory centers in the brain (left), and nerve connections that transmit the perceptions of food in the mouth and the nose to the brainstem and the brain (right).
The sense of taste, like the other senses, is especially fine-tuned to take notice of changes and differences. Having a superior ability to detect them is an important physiological function for the survival of humans as a species. It also adds to the enjoyment of eating by heightening awareness of the different types of food and the variety of flavors, stimulating our interest and whetting the appetite. This applies particularly to three separate aspects of the taste experience: intensity, congruency, and adaptation.
It is important to make the distinction between the intensity of a taste and the taste threshold. The intensity is the strength of a taste; the taste threshold of a substance is the lower limit at which it can be detected—for example, as determined by the concentration of the substance. Both of these aspects of taste vary from one individual to another and are linked to age, among other factors. On account of the synergy between different taste substances and their interaction with the sense of smell, it can be difficult to speak unambiguously about intensity and taste threshold. This relationship is exploited by cooks and gastronomes and, to its fullest extent, by companies making food products and snacks.
PERCEPTIONS OF COLD
Menthol, peppermint, and camphor are among the substances that can induce a false sensation of cold in the mouth because they have an effect on certain temperature-sensitive nerves even though the temperature in the oral cavity does not change. By way of contrast to this effect, there are substances that, while they are at the same temperature as the oral cavity, can cause, in a true chemical and physical sense, an actual drop in the temperature inside the mouth. This comes about because dissolving the substances in the surrounding saliva requires energy, which is taken from the saliva in the form of heat, with the result that the temperature drops in the mouth. Examples of this type of substance are the sweeteners xylitol and erythritol. Both, so-called sugar alcohols, sweeten about as much as ordinary sugar, but contain, respectively, 33 and 95 percent fewer calories. On the tongue, xylitol and erythritol crystals induce a surprisingly strong sensation of cold, which can be used to advantage in sweet desserts. As the drop in temperature is caused by the actual dissolving process, this effect is absent if these sweeteners have already been added to a liquid. Conversely, the effect of those substances that induce a false impression of cold persists even when they have been dissolved.
Individual taste substances can enhance one another if they are harmonious or complementary, which is known as having congruency. This can have the effect of lowering the taste threshold so that they can be detected at lower concentrations when mixed together than when present on their own. An example is sprinkling a little sea salt on dark, bitter chocolate, which makes it taste sweeter. Congruency also applies to the interaction between taste and smell, allowing either to be detected at lower concentrations. All cuisines avail themselves of these interactions, blending together complementary sensory perceptions to prepare dishes that are judged as being more flavorful.
When tastes marry
The Italians have a delightful way of referring to congruency. When tastes are complementary and enhance each other, they say Si sposa ben—They marry well
—or even Si sposa magnificamente!
Conversely, we often learn to like a whole range of foods that have tastes similar to those that we find unpleasant or that could potentially be inedible or harmful. After we have been exposed to them for a period of time, we can become accustomed to them—just think of curries so spicy that your eyes water; ice-cold desserts that almost hurt the teeth; or hot, bitter espresso. In these cases, we pay scant attention to potential danger signals emanating from taste and mouthfeel sensors, a phenomenon known as taste adaptation. This is also true of odors. We are rarely aware of the smell in our own home, but immediately become aware that there is a different smell when we step into a neighbor’s house.
The situation becomes even more complicated when we talk about a flavor impression as it is experienced by an individual. It is not simply a physiological matter encompassing all the sensory components of flavor. It also has social, psychological, psychosomatic, and cultural dimensions, which are linked to norms, upbringing, lifestyle, values, and identity. The actual physiological impression is merged in the brain with previous experiences, memory, and social context, transforming it into a very complex entity. Even though we eat food every day, flavor remains a concept that we have difficulty in describing to ourselves and to others.
Over the course of human evolution, the many different components of flavor, including mouthfeel, have been adapted to the chemical and physical properties of available ingredients to meet the daily challenge of feeding ourselves. To gain a better understanding of how all these gustatory elements can be combined to produce a multitude of effects, we will examine the chemical and physical properties of raw ingredients and prepared food, viewing them as our working materials, in the chapters that follow.
Mouthfeel: A Central Element of the Total Flavor Experience
Of all the different contributors to the total flavor experience, mouthfeel is probably the most neglected. We rarely pay much attention to the actual mechanical aspects of eating, which produce the tactile sensations on which mouthfeel is based. Chewing, the movements of the tongue and its examination of the feel of the food, breathing, and swallowing all proceed more or less automatically without our thinking about them unless the food diverges greatly from what we anticipated. This is an important aspect, because mouthfeel is a sense that is driven, to a great extent, by our expectations based on visual, olfactory, and tactile inputs. Perhaps we think that an apple will be crisp, that steaming soup is hot, that a chile sauce is spicy, or that pumpernickel bread has a coarse texture. These expectations will be weighed against the actual sensory impressions once the food is in the mouth, sometimes with surprising results.
Returning now to the situation described at the beginning of the chapter, let us look more closely at the role of the sensory system as a guardian of the vulnerable interior of our body. Every time we are about to eat or drink something, this system goes into action. First, we put our senses of sight and smell to work via the orthonasal pathway to evaluate whether the food or drink should come any closer to our mouth. Both of these sensory impressions, as well as how a substance feels in our fingers if we are holding it or by inspecting it with the help of knife, fork, or spoon, are merged together and conveyed to the brain. Here they are integrated with expectations, experiences, memories, and other psychological factors to produce an initial evaluation about whether to proceed any further.
If the brain sends a positive signal, but before the food is allowed to enter the actual oral cavity and stay there, it is next judged by physical contact with the lips, which sense its temperature and other characteristics, such as coarseness. All still being well, we put the food into our mouth, where the tongue and the inside of the mouth are ready to trigger a whole cascade of mouthfeel sensations. These help us avoid food that is undesirable because it is, for example, extremely hot or cold, seems to be poisonous, or so hard that it cannot be chewed or digested. The temperature of the food and its size and shape, as well as the nature of its surface, are then judged. If it is a liquid, its temperature and viscosity are noted. As soon as the food is in the mouth, odor substances reach the nose via the retronasal pathway, leading to a much more intense impression of smell than that based on the orthonasal pathway. It is still not too late to spit out the food or drink and any potential damage may have been averted, as it has not yet been swallowed. But sometimes these safeguards fail and many of us have experienced pizza burn
or the pain caused by a too-hot potato.
AN EXPERIMENT: WHEN EXPECTATIONS ARE NOT FULFILLED
Crisp potato chips (left) and ones that have gone soft (right)—they look the same, and their taste is identical, but their mouthfeel is completely different.
This is an experiment that can best be carried out with other people, using potato chips, crackers, or cookies. Prepare two types of food: one crisp, and the other soft. It is important that the two look as much alike as possible and that you or the others doing the tasting do not know which is which. First of all, look at the foods and try to judge how they will taste and feel in the mouth. Next, eat them and decide how your expectations were met and what effect this has on how you perceive their taste.
A similar experiment can be conducted with two similar-looking apples: one crisp and juicy, and the other dry, soft, and mealy.
Once the food is in the mouth, mechanical handling of the food takes over, while the salivary juices start to flow. If the food is a liquid, it might be swirled around in the mouth a few times before it is swallowed. If the food is quite firm, the chewing movement of the jaws and the teeth will reduce it to small pieces, while the tongue is carrying out acrobatic maneuvers that mix everything together. At the same time, more taste substances are released and dissolved in the saliva, diffuse in the oral cavity, and are picked up by the taste buds, while volatile substances drift up into the nasal cavity and activate the odor receptors, especially when we exhale. The taste grows more intense. The vibrations from the movement of the tongue and jaws give rise to noise that is transmitted through the jawbones and cranium.
While all these chemical and physical processes are taking place, the brain is fully engaged. Both conscious and subconscious physiological and psychological mechanisms participate in a complex judgment of the overall flavor impression and the way in which this impression sends signals about whether the food is edible, whether it is nutritious, whether it will satisfy the appetite, and how much of it we should eat. Memory, experience, and what we know about that particular food dominate the outcome of this process.
THE FATHER OF GASTRONOMY ON THE FUNCTION OF THE SENSES AND ON THE MECHANICS OF TASTE
Jean Anthelme Brillat-Savarin is often referred to as the father of gastronomy.
In his immortal work, The Physiology of Taste (1825), which has been in print continuously since it was first published, he makes the following comments about the function of the senses and on the mechanical aspects of taste: