Chemistry for the Holidays

By Adrian Dingle

Some Thanksgiving and Christmas Chemistry

There’s undeniably one time of year that brings out the baker in us all. In fact, I suspect that the vast majority of the baking that takes place in the United States in any given twelve month period happens between mid-November and late-December, when seemingly the whole country turns its attention to the gathering and eating rituals that are Thanksgiving and Christmas. Within those holidays there are some more granular traditions surrounding certain foods, and you’ll hardly need me to tell you the ones that I’m talking about. What’s less likely is that you’ve ever thought much about the molecules behind those flavors. That is until now. What follows reveals a little chemistry behind some of the traditional foods of fall and early winter in the USA.

Cinnamon

From an addition to apple ciders, pies, buns, and rolls, to countless other fall recipes, cinnamon might just be the quintessential spice of the season. The molecule that contributes most the taste of cinnamon is called (2E)-3-phenylprop-2-enal. That sounds quite complicated, and that’s why the formal, systematic names of such molecules often have easier, more descriptive names that help the non-scientists to get a handle on things. This one is better known simply as cinnamaldehyde. That name usually sits much better with most people, and the molecule looks like this.

Cinnamaldehyde

There are many ways to break down the complicated version of the name, but one of the simplest is to look at its ending, also called its suffix. You’ll see that the name ends in -al. In organic chemistry that nomenclature indicates a functional group called an aldehyde, i.e., the small group of atoms below. You’ll see that aldehyde group at the top of the molecule above.

Aldehyde functional group

The aldehyde group contains a carbonyl group (-C=O) with a hydrogen atom connected to the carbon atom. (The carbonyl group is one that we will see again in other spicy molecules). This helps to explain the trivial name, cinnamaldehyde which taken literally tells us that this is, ‘the aldehyde responsible for the taste of cinnamon’. Another interesting fact that often escapes the casual baker is that cinnamon falls largely into two different types. The first type comes mostly from China (where it is sometimes called cassia) and Southeast Asian countries such as Vietnam and Indonesia. The second type comes mostly from Sri Lanka. The former is more bitter, and imparts the bold flavor that one finds in candy that is marketed as “red-hot”; the latter is milder, gentler, and sweeter, and is usually significantly more expensive. The Chinese cassia contain a higher percentage of cinnamaldehyde.

Pumpkin

Pumpkin is a real ‘gotcha’ for most folks. If asked to describe the taste of pumpkin, many people are going to wax lyrical about the taste that is commonly known as ‘pumpkin pie spice’ and most definitely not the taste (or smell) of the actual vegetable itself. Pumpkin itself is a bready, mildly sweet, slightly sulfurous tasting pulp that isn’t spiced at all. In fact, some would say that it’s rather bland. Methylbutanal, methylpropanal, and pentanal are just a few of the molecules that contribute to the smell of pure pumpkin, and you’ll see that we get back to a whole bunch of those -al, or aldehydes, in that list. The (potentially unpleasant) sulfur notes are caused in part by dimethyl sulfide molecules, but taken altogether, those molecules don’t really give an especially distinctive set of aromas and tastes that make them much beyond “cooked vegetables”.

Getting back to the quintessential and ubiquitous fall “pumpkin spiced” flavor profile, we find that it is actually a combination of various other flavoring and spices. The combos can vary greatly, but typical mixtures have cinnamon, allspice, nutmeg, ginger, mace, and cloves. So, let’s take a closer look at some of those things, that together make the tastes that some people think of (incorrectly) as ‘pumpkin’.

Ginger

Whether it be gingerbread, ginger ale, ginger beer, ginger cake, or an important spice in the curry that makes those turkey leftovers so delicious, this famous spice is a vitally important one in cooking over the holiday period.

Ginger is known for its sometimes harsh, peppery, and strong flavor, but in reality, there is a wide range of pungency that it can deliver, depending on how the active chemicals are altered in various treatments. The group of molecules that are mostly responsible for ginger’s flavor are appropriately called gingerols, 6-gingerol being a prominent one.

6-Gingerol

However, you won’t be surprised to know that’s not its formal name, and also won’t be shocked to know that the real name is much less easy to swallow; (5S)-5-Hydroxy-1-(4-hydroxy-3 methoxyphenyl)decan-3-one. In this instance you’ll see a different ending to the name than the aldehydes mentioned above, this time the suffix being -one. Compounds which such endings to their names are called ketones, and they contain a functional group which is not dissimilar to the aldehydes mentioned previously, but with two carbon atoms connected to the aforementioned carbonyl group.

Ketone functional group

Ginger, and by that I mean 6-gingerol, is a pretty interesting compound, and its conversion to other similar molecules in differing circumstances really is very important. The gingerol in fresh ginger can be quite potent. However, cooks can turn up, or turn down, that quintessential spicy heat in a couple of simple ways.

Heating the gingerol converts it to a compound called zingerone, another ketone. This compound is less pungent than gingerol and explains why ginger loses some of its ferocious taste when baked in something like gingerbread.

Zingerone

On the other hand, dehydrating (drying) the ginger converts gingerol into compounds called shogaols. These compounds are more pungent in terms of their ginger flavors, and that explains why dried ginger is the more aggressive version of fresh, cooked, and dried.

6-Shogaol

Nutmeg

In addition to being a vital element of pumpkin spice, being added to German Spätzle, and a popular choice for topping rice-pudding, nutmeg has a vital role to play in the festive food season. You often see this complex, woody, earthy, floral, peppery, citrus based spice grated on top of that Christmas classic, eggnog.

As you may have guessed, nutmeg is a complex spice in terms of its chemistry, but one important chemical in the mix is myristicin.

Myristicin

Your humble nutmeg is perhaps not quite as innocent as it may first appear. Nutmeg has been known as a hallucinogenic material for some time, and myristicin was thought to be the molecule that caused the effect. However, the research has not been definitive, and it’s now thought that the effect may be more to do with a combination of compounds found in nutmeg such as elemicin and safrole.

Elemicin	Safrole

So, there’s a quick tour of some of the molecules that delight you over the holiday period. All those delicious treats are no more than chemistry at work.

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