Have you ever felt the inexplicable urge to open a book and inhale deeply between its pages? We do not know why, but that smell is pleasant to us. And we can’t help it. It doesn’t matter if it’s old or new, a children’s story from your little cousin or a Dostoyevsky classic. All of them are accompanied by a magical aroma. But why do books have that particular smell? And above all, why do we like it so much? Both questions have been answered by science.
A combination of ingredients. “A mixture of herbaceous aromas, with acid tips and a touch of vanilla on an underlying musty smell”: this is how Matija Strlic, Professor of Heritage Sciences at University College London, described the smell of books in his work Heritage odor: a framework for the identification, analysis and archiving of historical odors, from 2017. No one would think that the leaves we pass are made of mold or vanilla. And, actually, they are not, but as we will see later, the smell has a certain relationship.
Why? Mainly due to the degradation in time of certain products that make up the paper, especially lignin. Lignin is a natural biopolymer, one of the main components of plant biomass. That is, it is present in trees, shrubs and plants. When paper mills treat wood to make paper they extract the cellulose to create a kind of pulp and remove the hemicellulose and lignin.
They get rid of it because the latter in particular makes paper handling difficult due to its natural stiffness properties. But their separation is not total. “During the removal of lignin, some of its essential oils remain together with cellulose and that is what gives the paper its characteristic aroma. Aroma that, by the way, is also used in some perfumes”, they explain from the Institute of Chemical Technology of the Polytechnic University of Valencia.
We transform it into aroma. These remnants of substances that remain on the paper of a book, along with the passage of time, exposure to oxygen and humidity, gradually degrade it, causing that brownish appearance that we see when we open a volume from decades ago. Its leaves become brittle and easy to crack. This is what happens in libraries and archives, where certain books are no longer suitable for use by the general public. And the stronger the smell, the more unstable the paper is.
This paper contains different chemicals that the brain transforms into aromas. Among them are vanillin, which smells like vanilla; acetic acid, the smell of which resembles vinegar; short chain aldehydes that smell like dry grass; and benzaldehyde, to bitter almonds. “If you combine all of them, you will probably get something similar to caramel ice cream. Some of these components are also found in high-temperature processed foods, such as coffee or barbecue sauce,” the researchers explain.
For perfumes. In the past, lignin was a by-product, a waste from paper mills, but little by little it became something that is usable. Today, the chemical industry transforms it into aromatic compounds such as vanillin or vanillol for the production of perfumes or into the so-called BTX (benzene, toluene and xylene) that are then used to generate different chemical products or biofuels.
It is likely that with the technological advancement in the paper industry, paper will not age as it does right now and that one day we will stop having books that smell like that. But the smell of new books, a mixture of chemical components, ink and glue, also causes us an effect beyond the strictly olfactory.
It is not chocolate. To find out how humans perceive the smell of books, researchers at London College University conducted a study in which they extracted organic compounds from a 1928 French novel they found in an old bookstore. Volunteers blindly sniffed excerpts from the book, plus seven other unlabeled scents ranging from chocolate and coffee to fish market and dirty clothes. Subsequently, the participants completed a survey with a question asking them to describe the smell of the historical book.
Without knowing what they smelled, more than a third of the 79 participants said the book excerpt reminded them of chocolate. Coffee was the second aroma chosen. It may sound weird, yes, but chocolate and coffee contain fermented or roasted chemical compounds. That lignin and cellulose that we talked about before, which we also find in used paper.
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