What does Christmas smell like? The science behind warm, spicy holiday scents

The scents that surround us during Christmas and holidays derive from the essential oils of the various spices used in sweet and savory preparations or in decorations (think of the fir tree on the Christmas tree). They are responsible small volatile molecules (Volatile Organics Compounds, VOCs) emitted by spices, decorations and typical foods of the period, which easily evaporate and reach our nose. It is difficult to associate a specific scent with a single molecule, because they are the result of ainteraction between many different molecules (even hundreds!) which, combined in a specific way, represent a sort of olfactory fingerprint. From a chemical point of view, they belong to a large variety of classes of molecules: aldehydes and terpenes, but also phenols and organic acids. Some are also repeated in plants with completely different scents, confirming the fact that each combination is one of a kind.

The scent of decorations

From Christmas trees (usually a fir of the species Abies alba) and from the pine twigs of the floral decorations come fresh and pungent notes typical of conifers. The main culprits are two monoterpenes, α e β-pinenepresent in percentages ranging from 25% to 49%, both in the needles and in the resin of pines and firs. But we also find a perhaps better known molecule, the limonene (17-33%), also contained in oranges and lemons. The essential oil of the needles is also rich in bornyl acetate and camphenewhich give that fresh note to the smell of fir.

Cinnamon, the queen of sweets

You may not like it, but cinnamon (Cinnamomum verum) is present in many Christmas preparations and even in small quantities it manages to give a warm, sweet and enveloping to any dish. The drug (a term which in botany and pharmacognosy indicates the part of the plant used) is represented by the internal bark, which once dried it rolls up naturally on itself forming the sticks we know. The molecule that characterizes it most of all is la trans-cinnamaldehyde (an aldehyde), present in concentrations ranging from 70 to 80%! There are also eugenol, coumarins and cinnamyl acetate which contribute to the complex scent of this spice.

Orange omnipresent in Christmas recipes

Nothing of the orange is thrown away: candied fruit from the whole fruit, squeezed juice, jams from the pulp and peel, liqueurs, infusions (alcoholics such as mulled winebut also herbal teas) and air fresheners, both with fresh and dried fruit. Simply by pressing the peel of the Citrus aurantiuman essential oil rich in terpenes is released, first of all the limonene (85-90%), but also linalool, linalyl acetate and citral, which contribute to making its scent unique and differentiating it from other citrus fruits such as lemon or mandarin.

Cloves and nutmeg: similar molecules, different flavors

These two spices, widely used in both sweet and savory preparations, have totally different aromas and derive from plants that are not even remotely related: cloves (Syzygium aromaticum) belong to the Myrtaceae family, while nutmeg (Myristica fragrans) to that of the Myristicaceae. Yet the molecules responsible for their aroma are incredibly similar, to the point that they differ only in the position of a double bond between two carbons, as visible in the image: eugenol for cloves, isoeugenol for nutmeg! In nutmeg essential oil we also find an old friend, limonene.

The lustful scent of star anise

From the scent fresh and delicate and with its unmistakable star shape, also star anise (Illicium verum) is a component of mulled wine, as well as aniseed sweets and many potpourri preparations. The main component of the essential oil and therefore of the smell of star anise is an ether, the trans-anetholebut here too we find some old friends: limonene, α-pinene and linalool. The molecule that is most associated with its flavor is shikimic acid (yes, in chemistry we give funny names to things). Curious note: the genre Illicium to which star anise belongs together with green anise, derives from Latin and means “seduction”.

The aroma of chocolate

From the food of the gods, (a name, a destiny) this is the meaning of Theobroma cacaoyou get one of the must-have drinks for these cold evenings: hot chocolate. The enveloping notes that reach our nose derive from the process of fermentation and subsequent drying that fresh cocoa beans undergo. The molecules that form are pyrazines, derivatives of methylbutanal, which give that pinch of salty4-hydroxy-2,5-dimethyl-3(2H)-furanone, for the hint of caramel, dimethyl trisulphide, which recalls cooked cabbage (!!), and phenylacetaldehyde, with honeyed notes. The delicate harmony between these molecules has stimulated research since the early twentieth century, when Binbridge and Davies identified the first compounds in 1912: to date they have been identified over 500 compounds which form the chocolate aroma!

Vanilla through the centuries

The queen of vanilla flavor (Vanilla planifolia) is undoubtedly the vanillina small aldehyde (also theirs) which makes this spice unmistakable: according to Cortez, vanilla was already used by the Aztecs to flavor chocolate. It was isolated for the first time in 1858 by Gobley and soon the market demand for vanilla was so high that it began to be produced synthetically from eugenol. Today, however, almost all vanillin is produced from the lignin present in wood pulp waste in paper production. This synthetic vanillin is exactly identical to the one extracted from the vanilla pod, but the taste of vanilla can be different because, as with other spices, it also depends on the presence of other molecules which all together sing the taste melody of vanilla.

The smell of the fireplace crackling

When we light the fireplace, the combustion of wood degrades many molecular structures of the plant, forming compounds that make us think of winter and Christmas. The most common are phenols, acetophenone, benzaldehyde derivatives (aldehydes here too!), but it seems that one of them is linked to the smell of the fireplace: the syringol (or 2,6-dimethoxyphenol) a product of the pyrolysis of lignin, the polymer that guarantees resistance and solidity to plants. It is also the main aroma of smoked foods. As pleasant as a nice fireplace can be, remember that it is also a source of particulate mattermicroscopic particles that can be inhaled or get into our eyes causing breathing problems and red eyes.