That’s the delicious, comforting smell of an old book, according to a recent article from Analytical Chemistry (or the NYT), and of course, that wonderful smell means something bad. Dr. Matija Strlic researched what was behind this wonderful smell out of an interest of book preservation and set about y analyzing the volatile organic compounds they emit to see what they might reveal about the state old books were in.

Dr. Strlic said he got the idea one day at a library when he saw a conservator sniffing an old piece of paper, trying to determine what it was made of. “I thought, certainly a technique could be developed to do that more accurately,” he said. The approach is similar to breath analysis used to diagnose illness, he added.

He and his colleagues analyzed the volatiles produced by 72 samples of old paper of different types and in varying condition from the 19th and 20th centuries, using liquid chromatography-mass spectrometry. They found that some compounds were reliable markers for paper with certain characteristics — high concentrations of lignin or rosin, for example, which make paper degrade relatively quickly.

Portable devices that can detect volatile compounds already exist, Dr. Strlic noted. So with further research, he said, it may be possible to develop one for use in libraries and other places. Such an electronic nose would sniff the air around old books to find those that are so fragile they should not be lent out, for example, or are otherwise in need of preservation.