It’s beginning to smell a lot like Christmas...
Did you know? Pinene, a hydrocarbon derived from pine tree resin, can be used to make jet fuel.
Cut! Shouldn’t that be “look” like Christmas? For the traditionalists out there, sure. But for this scientific look at the holiday, I’m going to introduce you to a few of the molecules responsible for some common Christmas smells and tastes. It’s time to talk turkey… and gingerbread and trees.
O Tannenbaum, how lovely is thy pinene...
A decorated pine tree, twinkling with lights, is an iconic Christmas image. While I don’t want to debate the merits of artificial versus natural, there’s no denying that a fresh tree wins in the scent department. That cherished Christmas tree smell comes from pinene, a molecule found in a pine tree secretion called resin. Resin is a very viscous (thick) and sticky liquid secreted by trees that ends up hardening into a transparent solid.
Did you know? Clove oil has been tested as a dental painkiller. Its main component, eugenol, has analgesic (painkilling) and antibacterial characteristics.
Pine resin is mostly composed of hydrocarbons, which are molecules made up of hydrogen and carbon atoms. What smells good to us may actually help keep harmful insects away from plants. Resins may be also beneficial to trees by helping to seal and protect wounds.
Remember to leave out a delicious gingerol, eugenol and cinnamaldehyde cookie for Santa...
Whether they’re shaped like people or built into houses, gingerbread cookies are a spicy Christmas favourite. The three important gingerbread spices are ginger (no surprise!), cloves and cinnamon.
Ginger is the dried root of a perennial herb, grown mainly in China and India. Gingerol is the molecule most responsible for giving ginger root its sharp spiciness. When ginger is heated, gingerol loses a water molecule, producing a dehydrated variant called shogoal and another fragmented (shortened) variant called zingerone. Together, these three molecules produce ginger’s zingy aroma and flavour.
Did you know? Pinene, the molecule that makes your Christmas tree smell so good, is also the main component of turpentine (paint thinner).
The second gingerbread spice actually comes from a cousin of the Christmas tree. Cloves are the dried unopened flower buds of a tropical evergreen that grows mainly in Indonesia, Zanzibar, and Madagascar. Cloves have a pungent, sweet, almost hot aroma and taste that come from eugenol, the main component of clove oil.
The final gingerbread spice also comes from evergreens. Cinnamon is the dried bark of two closely-related tree species, one of which grows in Sri Lanka and India and produces Ceylon cinnamon. The other grows in China and produces Chinese cinnamon (also called cassia). Cinnamon sticks (also called quills) are curled up pieces of the trees’ bark. The molecule that gives cinnamon its sweet spicy "cinnamon-ness" is called cinnamaldehyde.
Chestnuts (and turkeys) roasting on an open fire...
Did you know? When food is burnt, rather than nicely browned, some products of the Maillard reaction can be harmful to human health. One example is acrylamide, a suspected carcinogen.
Fragrant and browned roast turkey is a definite Christmas classic. The browning of cooked food, as well as the delicious aroma and flavour that accompany the colour change, are caused by the Maillard reaction. Named after Louis-Camille Maillard, the scientist who first identified it in 1912, the reaction occurs when sugars and amino acids (the building blocks of proteins) are heated together. It should really be called the Maillard reactions (plural), since thousands of different products can be formed depending on exactly what kinds of sugars and amino acids are present and what temperature is used for cooking. For example, thiophenes are molecules that smell and taste meaty, while oxazoles are molecules that smell and taste nutty. Details aside, the molecules produced by the Maillard reaction provide all kinds of deliciousness.
All I want for Christmas is… molecules!
Whether you’re digging into roast turkey or gingerbread cookies this holiday season, you’ll have molecules to thank for all the aromatic goodness you encounter. Even pine-scented candles owe their aroma to pinene. Indeed, most of the molecules mentioned above are used commercially in purified form as flavouring agents or fragrances. Granted, you probably won’t find a perfume based on thiophene. Eau de Meat just doesn’t sound that appealing.
- Bokinsky G, Peralta-Yahya P et al. 2011. Synthesis of three advanced biofuels from ionic liquid-pretreated switchgrass using engineered Escherichia coli. Proceedings of the National Academy of Sciences of the United States of America. 108: 19949-19954. http://www.pnas.org/content/108/50/19949.full