Recently, a group of my colleagues were standing around reminiscing about Christmases past and the holiday season. One person commented that more than anything, the smell of cloves and nutmeg is the smell of Christmas to them.
That started everyone discussing the smells that we associate with the season - pine trees in the living room, decorated gingerbread houses, roasting turkey and mince meat pies. Our sense of smell is very powerful and the smells of our youth have a way of transporting us back in time.
Of course, most of the group was chemists and so our conversation shifted subtly to "what are the compounds that are responsible for our sensual pleasures at Christmas time and where do they come from?"
To begin with, it is necessary to understand our sense of smell. After all, our sense of smell has such a strong association with our memories.
There is nothing like the whiff of Christmas cake or the smell of a freshly-unwrapped candy cane for bringing forth such vivid memories and sensations. This is because our sense of smell is unfettered on the way to the brain. Within the nasal cavity are receptors that are the ends of neurons dangling from the brain. Yes, if you look up someone's nose hard enough, you can see their brain!
These neurons connect with the olfactory bulb but they also feed directly into the limbic system which is tied to our emotional self. There is very little processing of the signal between the nose and the brain which is understandable from an evolutionary point of view.
But this lack of processing is why the eugenol from cloves or the cinnamaldehyde from cinnamon are such evocative odors and can so easily conjure up memories from childhood. The molecules in the air that we smell trigger immediate responses in our brains.
Interestingly enough, these molecules can all be classified as volatile organic compounds or VOC's which have received a bad rap of late. VOC's are responsible for some of the malodourous events in our town and people generally speak of them as bad chemicals. Acrolein is an example of VOC.
However, everything that you can smell, from stinky perfumes to the delicious aroma of fresh baked cookies, is pretty much a result of VOC's.
Organic compounds are the chemicals that react with our olfactory neurons and produce a response. It is hard to smell inorganic scents and even harder to smell things that do not volatilize or become gaseous.
Christmas is also about taste which is a much more complex subject than smell.
Yes, we have the four traditional tastes on our tongues - sweet, salt, bitter, and sour - but we also have the aroma that our nose detects to aid in developing the taste of our food.
Recently, food scientists have even come to realize the important role that vision plays in our sense of taste. One of the more interesting experiments that can be done at home is to take some lemon Jell-O and add food dye to generate different colours.
If a person has their eyes closed, they will generally be correct in identifying the flavour but if they see the Jell-O, the colour will influence what they taste. Lemon Jell-O that has been dyed red tastes like strawberries and blue Jell-O tastes like blueberries.
Food chemistry is a relatively new science. Research into this area began in the early part of the 20th century with the French chemist Louis-Camille Maillard. He was interested in the reaction of sugars with amino acids. A mixture of serine and glucose, for example, smells like maple.
Since that time, chemists have worked out any number of flavours and can imitate the aroma of just about any food. However, as one noted food critic put it, the artificially-flavoured food always tastes a bit hollow.
The reason behind this is that taste is a combination of many senses and it is not just a molecule or two. Coffee, for example, has well over 4000 chemical compounds involved in its flavour. Its aroma is easily composed of over 500 volatile organic compounds.
The one or two compound versions of these tastes is a bit like listening to Beethoven's Fifth Symphony played on a recorder versus hearing a full orchestra. The full sense of taste and smell comes from the complex interaction of many different compounds.
Our noses and taste buds are filled with the smells and tastes of the season which is partly why Christmas is such a wonderful time of the year. Of course, if you have a winter cold, this time of year might not be as wonderful.
