The Chemistry Behind the Smell of Old Books: Explained with a Free Infographic

What gives old books that ever-so-dis­tinc­tive smell? Andy Brun­ning, a chem­istry teacher in the UK, gives us all a quick primer with this info­graph­ic post­ed on his web site, Com­pound Inter­est. The visu­al comes accom­pa­nied by this tex­tu­al expla­na­tion. Writes Brun­ning:

Gen­er­al­ly, it is the chem­i­cal break­down of com­pounds with­in paper that leads to the pro­duc­tion of ‘old book smell’. Paper con­tains, amongst oth­er chem­i­cals, cel­lu­lose, and small­er amounts of lignin – much less in more mod­ern books than in books from more than one hun­dred years ago. Both of these orig­i­nate from the trees the paper is made from; fin­er papers will con­tain much less lignin than, for exam­ple, newsprint. In trees, lignin helps bind cel­lu­lose fibres togeth­er, keep­ing the wood stiff; it’s also respon­si­ble for old paper’s yel­low­ing with age, as oxi­da­tion reac­tions cause it to break down into acids, which then help break down cel­lu­lose.

‘Old book smell’ is derived from this chem­i­cal degra­da­tion. Mod­ern, high qual­i­ty papers will under­go chem­i­cal pro­cess­ing to remove lignin, but break­down of cel­lu­lose in the paper can still occur (albeit at a much slow­er rate) due to the pres­ence of acids in the sur­round­ings. These reac­tions, referred to gen­er­al­ly as ‘acid hydrol­y­sis’, pro­duce a wide range of volatile organ­ic com­pounds, many of which are like­ly to con­tribute to the smell of old books. A select­ed num­ber of com­pounds have had their con­tri­bu­tions pin­point­ed: ben­zalde­hyde adds an almond-like scent; vanillin adds a vanil­la-like scent; eth­yl ben­zene and toluene impart sweet odours; and 2‑ethyl hexa­nol has a ‘slight­ly flo­ral’ con­tri­bu­tion. Oth­er alde­hy­des and alco­hols pro­duced by these reac­tions have low odour thresh­olds and also con­tribute.

The Aro­ma of Books info­graph­ic can be viewed in a larg­er for­mat here. And because it has been released under a Cre­ative Com­mons license, it can be down­loaded for free. For anoth­er expla­na­tion of this phe­nom­e­non — this one in video — see this pre­vi­ous post in our archive:  The Birth and Decline of a Book: Two Videos for Bib­lio­philes

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via IFLScience

Relat­ed Con­tent:

A Secret Book­store in a New York City Apart­ment: The Last of a Dying Breed

Old Books Bound in Human Skin Found in Har­vard Libraries (and Else­where in Boston)

Spike Jonze Presents a Stop Motion Film for Book Lovers

Wear­able Books: In Medieval Times, They Took Old Man­u­scripts & Turned Them into Clothes

13-Year-Old Char­lotte Bron­të & Her Broth­er Wrote Tee­ny Tiny Adven­ture Books, Mea­sur­ing 1 x 2 Inch­es