The older the books the more they smell of furfural
The odour of books is a result of a complex mix of volatile chemicals produced by chemicals used in their manufacture, as well as the gradual degradation of the chemicals within the paper. Furfural is one of them. Of course, older books contain a higher amount of hemicelluloses, which would be the source of furfural.
Therefore, it can be used to determine the age and composition of books, with..
..books published after the mid-1800s emitting more furfural, ..
..and its emission generally increasing with publication year relative to older books composed of cotton or linen paper.
References: The expert panel of FEMA (Flavor and Extract Manufacturers’ Association) assessed Furfural as GRAS (generally recognised as safe). See DOWNLOADS.  www.businessinsider.com