A Merry Molecular Christmas

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Krysta Levac
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8.6

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Many holidays mean delicious food - and smells! This fun article looks at the chemistry behind the common aromas of Christmas.

It’s beginning to smell a lot like Christmas…

Some of the products of the Maillard reaction include furans, furanones, pyrazines and thiophenes
Some of the products of the Maillard reaction include furans, furanones, pyrazines and thiophenes (Source: Andy Brunning [CC-BY-NC-ND] via Compound Interest). ​

Cut! Shouldn’t that be “look” like Christmas? For the traditionalists out there, sure. But for this scientific look at the holiday, let’s learn about some of the molecules responsible for some common Christmas smells and tastes. It’s time to talk turkey, gingerbread, and trees.

Chestnuts (and turkeys) roasting on an open fire

Fragrant and browned roast turkey definitely a Christmas classic. The browning, the delicious aroma and flavour are all caused by the Maillard reaction. That’s a chemical 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 probably be called the “Maillard reactions” (plural), since there are thousands of different products that can form. Which product forms depends on two factors:

  1. The kinds of sugars and amino acids present

  2. The temperature at which they are cooked

For example, thiophenes are molecules that smell and taste meaty. Oxazoles are molecules that smell and taste nutty. Details aside, the molecules produced by the Maillard reaction provide all kinds of delicious flavours.

Did you know?

Some products of the Maillard reaction aren’t good for you. This is especially true when food is burnt instead of nicely browned. One example is acrylamide, a suspected carcinogen.

O Tannenbaum, how lovely is thy pinene?

Molecules that contribute to the smell of Christmas trees include bornyl acetate, alpha-pinene and beta-pinene
Molecules that contribute to the smell of Christmas trees include bornyl acetate, alpha-pinene and beta-pinene (Source: Andy Brunning [CC-BY-NC-ND] via Compound Interest).

A decorated pine tree, twinkling with lights, is an iconic Christmas image. Every Christmas, many households have the same debate: should we get an artificial tree or a natural tree? There’s no denying that a fresh tree wins in the scent department. The cherished Christmas tree smell comes from pinene, a molecule found in resin. Resin is a very viscous (thick) and sticky liquid secreted by trees. It ends up hardening into a transparent solid.

 

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 the plants that produce them. Resins may also help trees seal and protect wounds in their branches and trunks.

Did you know?

Pinene is also a major component in chemicals such as turpentine and jet fuel!

Remember to leave out delicious cookies for Santa

The compound gingerol provides the ginger flavour and zingerone is responsible for the spiciness of gingerbread cookies
The compound gingerol provides the ginger flavour and zingerone is responsible for the spiciness of gingerbread cookies (Source: Andy Brunning [CC-BY-NC-ND] via Compound Interest).

Whether they’re shaped like people or built into houses, gingerbread cookies are a tasty Christmas favourite. The three most important spices in gingerbread 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. This produces producing a dehydrated variant called shogaol and another fragmented (shortened) variant called zingerone. Together, these three molecules produce ginger’s aroma and flavour.

 

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, borderline-hot aroma and taste. These come from eugenol, the main component of clove oil.

Did you know?

Clove oil has been tested as a dental painkiller. Its main component, eugenol, has analgesic (painkilling) and antibacterial characteristics.

The compound cinnamaldehyde is used in many holiday baked treat
The compound cinnamaldehyde is used in many holiday baked treat (Source: Andy Brunning [CC-BY-NC-ND] via Compound Interest).

The final gingerbread spice also comes from evergreens. Cinnamon is the dried bark of two closely-related tree species. One of them grows in Sri Lanka and India and produces Ceylon cinnamon. The other grows in China and produces Chinese cinnamon (also called cassia). Cinnamon sticks (or “quills”) are curled-up pieces of the trees’ bark. The molecule that gives cinnamon its sweet-spicy flavour is called cinnamaldehyde.

All I want for Christmas is… molecules!

Every holiday season, we have lots of different molecules to thank for all the aromatic goodness around us. Even pine-scented candles owe their aroma to a molecule. In fact, most of the molecules you just read about are also used as flavouring agents or fragrances. Most, but not all. After all, you probably won’t find a perfume based on thiophene. “Eau de Meat” just doesn’t sound all that appealing!

Starting Points

Connecting and Relating

  • What smells and flavours remind you of special holidays?

  • Do you agree with the use of molecules, such as those discussed in the article, as flavoring agents in food? Why or why not?

  • Does it matter to you if a flavouring is naturally-derived or artificially-produced (e.g., vanilla)? Explain.

  • Would you eat food that is burnt, knowing that it may be harmful to human health? Why or why not?

Connecting and Relating

  • What smells and flavours remind you of special holidays?

  • Do you agree with the use of molecules, such as those discussed in the article, as flavoring agents in food? Why or why not?

  • Does it matter to you if a flavouring is naturally-derived or artificially-produced (e.g., vanilla)? Explain.

  • Would you eat food that is burnt, knowing that it may be harmful to human health? Why or why not?

Relating Science and Technology to Society and the Environment

  • Should industry be permitted to use artificial flavor or odor molecules to sell products that may be unhealthy (e.g., snack foods)? Why or why not?

  • In the future, movies may include scents that the audience could smell to enhance the viewing experience. How do you think theatres could create this effect?

  • Why do you think people add scents to certain products such as food, shampoo, etc.? Are there certain products that have become overly scented? For example, is it necessary to have laundry that stays scented for weeks? 

  • With growing concern over allergies to scents, do you think all products should have scent-free options? Would scent-free products be as appealing to a consumer? 

Relating Science and Technology to Society and the Environment

  • Should industry be permitted to use artificial flavor or odor molecules to sell products that may be unhealthy (e.g., snack foods)? Why or why not?

  • In the future, movies may include scents that the audience could smell to enhance the viewing experience. How do you think theatres could create this effect?

  • Why do you think people add scents to certain products such as food, shampoo, etc.? Are there certain products that have become overly scented? For example, is it necessary to have laundry that stays scented for weeks? 

  • With growing concern over allergies to scents, do you think all products should have scent-free options? Would scent-free products be as appealing to a consumer? 

Exploring Concepts

  • What is a Maillard reaction? What are some culinary terms that we use to describe or represent a Maillard reaction?

  • Why is pine resin important for a pine tree? 

  • Aside from the scents and flavours discussed in the article, choose your favorite scent or flavouring and research the molecules that produce this scent.

  • Choose one of the 6 molecules discussed in the article and create a product (real or imaginary) that can use this molecule for a purpose other than smelling good (For example, thiopene used in poison for insects, etc.).

Exploring Concepts

  • What is a Maillard reaction? What are some culinary terms that we use to describe or represent a Maillard reaction?

  • Why is pine resin important for a pine tree? 

  • Aside from the scents and flavours discussed in the article, choose your favorite scent or flavouring and research the molecules that produce this scent.

  • Choose one of the 6 molecules discussed in the article and create a product (real or imaginary) that can use this molecule for a purpose other than smelling good (For example, thiopene used in poison for insects, etc.).

Teaching Suggestions:

  • This article can be used to support teaching and learning of Chemistry and Food & Nutrition related to organic chemistry. Concepts introduced include Maillard reaction, sugars, amino acids, theophenes, oxazoles, pinene, ginger, gingerol, shogaol, zingerone, cloves, eugenol, cinnamon and cinnamaldehyde.

  • This article can be used in Chemistry to demonstrate the source, value and practical application of organic molecules. 

  • For an organic chemistry focus, teachers could have students look at the chemical structure and classify each of the scents and flavours mentioned in the article. 

  • For a food and nutrition class, teachers could have students read the article and then make recipes that use specific flavouring molecules, or create their own original recipe that incorporates a specific flavouring or chemical reaction (e.g., Maillard reaction) that creates a particular flavour.

  • To focus on the STSE issues related to scents, teachers could have students debate the positive and negative aspects of using scents in commercial products, using a Pros & Cons Organizer learning strategy. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats. 

Teaching Suggestions:

  • This article can be used to support teaching and learning of Chemistry and Food & Nutrition related to organic chemistry. Concepts introduced include Maillard reaction, sugars, amino acids, theophenes, oxazoles, pinene, ginger, gingerol, shogaol, zingerone, cloves, eugenol, cinnamon and cinnamaldehyde.

  • This article can be used in Chemistry to demonstrate the source, value and practical application of organic molecules. 

  • For an organic chemistry focus, teachers could have students look at the chemical structure and classify each of the scents and flavours mentioned in the article. 

  • For a food and nutrition class, teachers could have students read the article and then make recipes that use specific flavouring molecules, or create their own original recipe that incorporates a specific flavouring or chemical reaction (e.g., Maillard reaction) that creates a particular flavour.

  • To focus on the STSE issues related to scents, teachers could have students debate the positive and negative aspects of using scents in commercial products, using a Pros & Cons Organizer learning strategy. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats. 

Learn more

What is the Maillard Reaction? (2013)

This Scientific American video (2:10 min.) gives an introduction to the Maillard reaction, how it influences the taste of cooked foods, and the possible evolutionary reason behind it.

Seven Ways That Chemistry Puts The Magic Into Christmas (2014)

Article from The Conversation discussing the ways that the chemistry of Christmas can impact all the senses, and not just those of smell and taste! 

References

Burnham, P. M. (2006, August). Cinnamaldehyde. Hillsborough College.

Compound Interest. (n.d.). Christmas.

Extance, A. (2018, November 19). The marvellous Maillard reaction. Chemistry World.

Helmenstine, A. M. (2018, February 8). Why Christmas trees smell so good. ThoughtCo.

U.S. Forest Service. (n.d.). Resins.

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