Old books smell of vanilla

Modern paper is made from wood pulp, and wood contains lignin, a polymer that breaks down over the years. As it degrades it releases volatile compounds, and among the most prominent are close relatives of vanillin, the molecule behind vanilla's aroma.

That's why old books give off that unmistakable sweetish scent, mixed with notes researchers have described as grassy, almondy and faintly acidic. A team of conservation chemists went as far as analysing the gases old books emit to diagnose their state of decay: the smell literally tells you how much life the paper has left.

So the nostalgia that hits you in a second-hand bookshop has a chemical formula. Every book ages by perfuming itself with its own decomposition. The poetic and the scientific, on the same shelf.