Our knowledge of the past is odourless. Yet, smells play an important role in our daily lives: they affect us emotionally, psychologically and physically, and influence the way we engage with history.
In this work, we propose that smells are part of our cultural heritage, and that a structured approach to researching them is required. Several aspects allow us to explore the connection between olfaction and heritage. We will define heritage smells and argue their importance, by focusing on the following: (1) a theoretical review of olfaction and odours in heritage, including (a) the consideration for smells in heritage documents and guidelines, leading to the identification of smell as part of cultural significance of a place or object and (b) the use of smell in a heritage context as a means to engage and communicate with the audience; and (2) techniques for identifying, analysing and archiving smells and therefore enabling their characterization and preservation. These techniques can be approached from two complementary angles: firstly, the chemical analysis of the source of sensation, in our case chemical analysis of the compounds that lead to perception of the smell. Secondly, sensory characterization of that smell in terms of human perception. In the case of historic smells, this dual approach can contribute to a holistic understanding of what the odour represents in terms of the nature, history and state of the object.
The significance of olfaction in the context of cultural heritage, evidencing that smells can be fundamental in shaping who we are, where we belong and how we experience encounters with different cultures, has been recently examined in several case studies. They show that odour can be part of the local identity through history ; that a central place for olfactory experiences in a culture results in a much wider vocabulary to discuss smells  and that travel and tourism offer an opportunity to approach the world with our noses . However, the role of smells in our perception of and engagement with the past has not been systematically explored.
In the heritage context, experiencing what the world smelled like in the past enriches our knowledge of it, and, because of the unique relation between odours and memories, allows us to engage with our history in a more emotional way . Odours are also powerful cues to remember an exhibition, as demonstrated by Aggleton and Waskett  in their work at the Jorvik Viking museum in York, England. In the case of a gallery, the presence of point-of-scent components heightens the enjoyment of the public, in comparison to experiencing the same displays without smells .
However, unlike some food and culinary practices, smells are not recognized in the definition of intangible cultural heritage by UNESCO. In spite of sharing a relation to other aspects of intangible cultural heritage, such as language, industries, and tourism , the olfactory world is hardly discussed or documented.
Specific smells can also be related to cultural practices, expressions and knowledge. As an example, the art of Asian perfumery is threatened by industrialization and may be in need of protection. The smells carry the information about how practices have evolved throughout history, the materials associated with them and the conditions in which smells were experienced . In this case, smells are associated with intangible practices, although they still emanate from a tangible source, as knowledge has no smell.
The case for the smell of books as a case study is strengthened when the cultural significance is coupled with the research conducted on the volatile organic compounds (VOCs) constituting the aroma of historic books as a non-destructive diagnostic tool for paper degradation [34, 57], which the next section will address further.
At a time where the first olfaction-related inclusion into the UNESCO intangible heritage list is being considered, the discussion around the cultural significance, analysis and preservation of historic smells is highly relevant.
This work has argued that smells can be considered part of our intangible heritage, and that a definition of heritage smells requires an exploration of the relationships aromas have with other aspects of cultural heritage, such as, local practices and traditions, and language.
Anthropologist David Howes is one of the pioneers in the field of sensory studies, and the co-founder of the Centre for Sensory Studies at Concordia University. With this centre, Howes and sensory historian Constance Classen have created an open, yet robust space for exploratory and fundamental research into the cultural history of the senses.
This breaking down of large environmental ecosystems into synthetic representations, which still retain some memory or meaning is both part of modernity and embedded in our twenty-first century lives. It is, therefore, important to recognize, this as well as the role of personal memory, if we are to appreciate what is culturally shared and/or different in the places we construct. Tracing the history of pine scent thus gives us an insight into the breakdown of environmental features into their constituent parts as part of the process of becoming modern, and the move of pine as a therapeutic agent via the institution to the home. However, despite this industrialization of nature which is mirrored by the microscopic understanding of bodies and disease agents into ever smaller parts, cultural connections remain. The forest is still represented in our associations and emotions and thereby retains more meaning than a mere sniff from a bottle would suggest.