The smell of a public library is unmistakable.
It could be the random scents of hundreds of people moving in out and around or the homeless people lingering about or the products used to clean the tables, vacuum the floors and dust the shelves but every library does have the same familiar scent.
But is it the books giving off the strongest aroma?
Old book smell is a very real, and oddly, very important thing.
Old book smell isn’t figment of your imagination or nostril. New books all seem to smell the same — fresh ink, crisp paper and traces of the packaging — are usually the culprits. Old books, however, give off a much different and distinct odor. Some bound books carry a stronger scent than others and the old book smell depends on the age of the book.
Before the science behind the stench let’s discuss why it’s so vital to analyze the stink of a book. Old book order helps to determine the age of books. While books published for the past hundred years or so come with a handy printed date to verify publish dates, many important pieces of literature don’t come with a handy time stamp.
There’s a reason for this, as it’s been investigated as a potential method for assessing the condition of old books, by monitoring the concentrations of different organic compounds that they give off. As a result, we can be a little more certain on some of the many compounds that contribute to the smell.
Furfural, a compound included in the book funk, is useful in determining the age and composition of books. Works published after the mid-1800s usually emit more furfural. The older the book, the more pungent the old book smell. The furfural emission increases with publication and isn’t as strong on the older books printed on cotton or linen paper.
Old book smell and why people care
Now that we’ve got the “why should we care?” out of the way, here’s the “why the hell does it happens?” and what makes old books smell. I failed science and chemistry numerous times so I’ll let smart people explain.
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.
So the next time you’re in the library and wonder “why does this copy of Moby Dick smell literally like whale penis?” you can blame chemical degradation or the dirty people who take out library books for the old book smell. Neither would be wrong.
[via CompoundChem]