Sarah Everts and Harold McGee go on olfactory adventures

Who would have thought that sweat and the chemistry behind it could be so interesting? I’m glad that my former colleague Sarah Everts knew better than most of us and decided to write a book about it.

If you’ve been reading C&EN for some years, you will recognize Everts’s name because she was C&EN’s European correspondent for more than a decade. To learn more about the idea behind her book on sweat and what she has been up to since leaving C&EN, read the interview that reporter Megha Satyanarayana conducted with Everts for this issue (see page 24).

But let’s talk more about smells and the chemistry behind them. Everts is not the only one fascinated by odor. In fact, I just finished reading Nose Dive: A Field Guide to the World’s Smells, by Harold McGee, an award-winning author and expert in the science of food and cooking. McGee, for the purpose of this book at least, sees the world through smells.

In Nose Dive, he explores the science behind the smells around us, including the mouthwatering smells of food and wine, the common aroma of fresh pavement or freshly cut grass, and the rarer fragrance of truffles and ambergris. Nose Dive provides a guide to the “osmocosm,” a word derived from the Greek terms osme, meaning “odor” or “smell,” and cosm, meaning “world” or “universe.”

The book is a five-part affair, with part 1 dedicated to the “simplest smells.” For this, McGee goes back 14 billion years ago, to the “birth of the cosmos as a whole and the origins and evolution of life on Earth.” As the universe expands after the big bang, the first chemical compounds start “cooking up.” Primordial species made up of three to four atoms, such as H₂S, SO₂, NH₃, and O₃, would have created a sulfurous, sharp, and pungent odor. Had people been around, they would have been able to detect the compounds’ presence by smell, as these are some of the simplest cosmic molecules for which we have receptors. Conversely, other simple molecules, such as water, carbon dioxide, and nitrous oxide, would have gone largely undetected by smell because humans do not have receptors for those molecules.

Part 2 focuses on the smell of animal bodies, which is owed in no small part to the communities of microbes that animals carry with them.

Part 3 covers plants, which McGee refers to as “brilliant chemists” that “advanced the possibilities of the volatile far beyond the mineral and animal worlds.”

As you would expect, cilantro makes an appearance here. If an herb could be described as controversial or polarizing, cilantro is that herb, with cilantro haters saying it smells and tastes soapy.

Part 4 explores the smells that emanate from soil and water. In this section, a considerable amount of space is dedicated to fungi, including mushrooms and truffles. Truffles are expensive and highly coveted fungi because of the bouquet of fragrances and flavors they deliver. Typically, their aromas consist of sulfur compounds—such as dimethyl sulfide and disulfides—that give them garlicky, oniony, meaty smells, combined with other carbon chains and rings—such as octenol or ethylphenol—that add a nutty, fruity, leathery aroma.

Part 5 indulges in what McGee calls “chosen smells,” the fragrances of food, drink, and perfumes. He tells us about “the strangest of all fragrance materials,” ambergris, a waxy substance that originates in the intestines of sperm whales. The whales’ inability to eliminate indigestible squid parts causes obstructions that over time become a valuable substance whose aroma is defined by two polycyclic fragments: naphtofuran and ambrinol.

Smells trigger memories and emotions, and Nose Dive is a continuous evocation. A true olfactory adventure.

Views expressed on this page are those of the author and not necessarily those of ACS.