The distance between food science and the food media seems to be growing daily. Food scientists study foods, not just processed foods, but all types of foods. Food chemists describe the composition of food, what happens to raw food during handling, processing, and cooking in a manufacturing plant, restaurant, or home. Food toxicologists and microbiologists investigate the safety of foods from its chemical composition, the microbes it contains, and how to ensure its safety. Sensory scientists learn about how humans react to different foods with respect to flavor, appearance, and texture. Nutritionists assess the composition of the food with respect to calories, vitamins, minerals, and other nutrients. Dietitians translate this knowledge into healthy dietary patterns that fit within our personal culture. Food journalists help put all this information into understandable bits that we can incorporate into our daily lives. All of these technical perspectives can be quite confusing.

This post is written from the perspective of a food scientist who believes that somewhere along this vast journey important points disappear. To continue a series of posts on Lessons in Food Chemistry, I address chemical smells. Contributing to our appreciation of food are its flavor and the texture of that food in our mouth. We experience flavor through its smell and its taste. We smell food during its preparation at home or in a restaurant or as we open a packaged product. That odor can produce a pleasant experience that we associate with distant memory or stimulate our senses to appreciate a snack or meal to come. Once in the mouth three senses combine to contribute to the flavor experience:

• Taste—confined to sweet, sour, bitter, salty, or umami;
• Smell—bringing a multitude of odor sensations that help define our reaction to a specific food; and
• Mouthfeel—contributing to an appreciation of the smoothness, hardness, softness, brittleness, creaminess, crunchiness or other textural feelings we enjoy as we eat.

Chemical smells. The American public has developed an aversion to chemicals. Chemicals are considered to be bad things that we don’t want in our foods, in our bodies, on our hands, or in our air. We are becoming tolerant of molecules and what they can do for us. Although there are subtle differences in the meanings of chemical and molecule, when used in articles about food or medicine, chemicals have a negative connotation and molecules a positive one. When used in a news article, an ad, or in common conversation references to a chemical or a molecule differ primarily to whether the substance is considered harmful or beneficial. And yet, in common usage, the two words are interchangeable. From a scientific perspective everything we smell is the result of a molecule going up our nose, either through our nostrils or the back of our throat during chewing, to make a chemical connection. This connection sends chemical signals to the brain resulting in interpretation of the sensation. Thus, every smell we perceive is a chemical smell.

Objectionable aromas include what many of us think of when we call them chemical smells. A prominent category of these odors includes solvents such as acetone, benzene, chloroform, or methanol. Concentrated hydrochloric, nitric, and sulfuric acids produce noxious fumes. Experiences in high school or college chemistry labs prejudice us against such concentrated odors. Household bleach, or sodium hypochlorite, is not perceived as pleasant by our olfactory system. Hydrogen sulfide is an aromatic gas we pass when our digestive system is out of our control. Methyl sulfides are primarily responsible for the foul odor of human feces. Methylamine and cadaverine are foul odors in foods spoiled by bacteria. Hexanoic acid, hexanal, and heptanal are some of those compounds associated with rancid odors. All objectionable aromas are chemical smells.

Fruity and spicy aromas elicit much more pleasant responses in our noses. Some fruits and spices convey their odors through single molecules known as character-impact compounds. Sniffing a vial containing the chemical iso-amyl acetate communicates banana. The character-impact compounds for peaches are decalactones, but other compounds contribute to more subtle differences.  Benzaldehyde is the character-impact for tart cherries, but the chemistry of sweet cherry aroma is more complex. Tomatoes (yes, a tomato is a fruit) lack a molecule that provides character impact, but a complex mix of compounds stimulates our noses with that characteristic odor. Among those chemicals contributing to ripe tomato aroma are ethanol, methanol, pentenal, and geranylacetone.

Spices tickle our noses and fancies. Clove aroma is primarily eugenol. A related molecule, methyl eugenol, provides the character impact of basil pesto. Vanillin gives us the sensation of vanilla bean, but it is only the main chemical contributing to the aroma we perceive in pure vanilla extract. It comes as a surprise that the main odorant in almonds is benzaldehyde, even though it doesn’t smell like cherries. A sniff while holding some almonds under the nose with eyes closed can produce a faint version of the smell of cherries. All enjoyable aromas from fruits and spices are chemical smells.

Home food prep induces mostly pleasant aromas. Home cooks pride themselves in their ability to chop vegetables while wielding sharp knives when preparing delicious dishes. During that process, many vegetables emit odors that stimulate our olfactory sensors. One powerful aroma that is not so pleasant comes from chopped onions. Alkenyl-thiosulfinates are the molecules that predominate in producing these pungent odors. A short treatment in the microwave can decrease the pungency of the onion with a potential flavor loss in the finished dish.

Benzopyrenes contribute to the pleasant aroma of grilled meats. Although such molecules are carcinogenic, who can resist a fresh-grilled steak or hamburger? Not me! Any heating process induces a major transformation in the molecular composition of a food. Think of the wonderful color and flavor changes as white food turns brown during frying or baking. Color and flavor changes of these foods are due to Maillard browning, another possible hazardous process performed in home kitchens and processing plants. Any differences in flavor between a raw food and a cooked one is due to chemical modification of natural precursors to delectable heat-induced compounds that please our palates. All of the aromas emerging from the oven during cooking are chemical smells.

Processing contributes to flavor complexity in foods. Think chocolate, coffee, or wine processes which develop complex, subtle flavors that tickle our palates. Other processes like canning can decrease the complexity of product flavor while preserving the stability of a product. Freezing tends to maintain the delicate aromas of fresh fruits and vegetables. Drying concentrates certain aromas while producing others either through heat or bring molecules closer together so they can interact to produce new ones.

Then there are the formulated foods, also known as ultraprocessed foods. Formulated foods are mixtures of ingredients, analogous to foods prepared at home from a recipe. Most operations in the processing plant or steps in the kitchen foster the interaction of molecules within a food. Chances are that home cooks who use more than five ingredients to prepare a dish are fixing a homemade, ultraprocessed food. Don’t be fooled by single ingredients in the list that come with numerous ingredients. Most sauces, syrups, and condiments, whether homemade or storebought turn a five-ingredient meal into a homemade ultraprocessed food.  The objection to ultra-processed foods is not necessarily the degree of processing as it is the presence of chemical additives as ingredients. Any aromas emanating from an ultra-processed food is a chemical smell.

And let us not forget the so-called fake meats. Storebought fake meats are by definition ultraprocessed foods. Plant-based meat products extract proteins from plant sources such as soy, rice, peas, lentils, chickpeas or sunflower. Such extractions require multiple steps and are the major ingredients that require true ultraprocessing. Still, it is not these ingredients that draw ire from most critics. Sugar and salt are the two components most challenged by critics despite their classification by NOVA as processed culinary ingredients, and do not contribute to classifying a food as ultraprocessed. By replacing animal-based proteins with plant-based counterparts, fake meats and similar alternatives to milk and eggs, provide a more sustainable and potential healthier option to real meat, dairy, and poultry products. Any odor produced when preparing a fake-meat product is a chemical smell.

Consideration for those individuals who have impaired odor detection. Lack of the sense of smell may not be as dramatic a disability as blindness or deafness, but it can have major consequences on quality of life. Sure people experiencing anosmia avoid the unpleasant aromas, but they can’t fully appreciate the delicate aromas and flavors of a food. They can’t smell smoke as a warning of a fire, tell if they need a bath, or detect food spoilage. Partial or total loss of the sense of smell can be brought about by a physical accident or a lingering disease. I became sensitized to the hazards of anosmia through two friends—one lost her sense of smell after a bicycle accident and the other from an asymptomatic case of long COVID.

Take home lessons. Everything we put into our mouths is chemical. Every odor that finds its way up our nose is a chemical odor. Every process in a food formulation or step from a home recipe induces chemical reactions in the final food and major changes in the chemical composition of that food. Food scientists, restaurant chefs, home cooks, and normal people, unless burdened with full anosmia, experience chemical smells as all smells, good and bad, are chemical smells.

Coming soon to an electronic device near you:

 You want me to eat What? Edible Insects and American disgust!