The Chemistry of Thanksgiving Dinner

Elementary / Middle School / High School

If you’re like us at Ward’s, you probably stuff yourself silly at Thanksgiving. Turkey … mashed potatoes … gravy … name your favorite Thanksgiving food.

But Thanksgiving isn’t a day off from science! Science never sleeps (even from tryptophan—which we’ll talk about in a minute).

Here’s the chemistry of Thanksgiving dinner, including a few miscellaneous morsels of myth-busters and holiday “how to.”

Dig in…

Does Tryptophan Really Make You Sleepy?

So, you’ve eaten an entire Turkey leg (and countless other goodies) and now you're noticing the button on your pants is perilously close to bursting. What do you do?

You do what any normal person does: you unbutton your pants and lie on the couch for a good nap, cursing (or blessing) the tryptophan that’s making you so sleepy.

But is it really the tryptophan?

Here are the facts:

The Truth About Tryptophan

Tryptophan is an amino acid that’s a precursor to the brain chemical serotonin, which in turn is converted into melatonin, which helps you fall asleep. Turkey contains tryptophan, but many other foods contain tryptophan in similar amounts. Gram for gram, cheddar cheese actually contains more tryptophan than turkey does.

Tryptophan competes with all of the body’s other amino acids to enter the brain through a strict gatekeeper known as the blood-brain barrier. It’s the heaps of carbohydrates—the stuffing, potatoes, and yams smothered in marshmallows—that are the real culprit.

Consuming carbs triggers the release of insulin, which removes most amino acids from the blood—but not tryptophan. The lack of competition allows tryptophan to enter the brain and form serotonin, and, ultimately, melatonin.

Basically, any big meal containing tryptophan and lots of carbohydrates can trigger sleepiness—not just turkey (and when consumed on an empty stomach, tryptophan can lead to more vivid dreams!).

What Causes Heartburn?

Your stomach normally produces acid to digest food. If you eat a lot of food, your body overproduces acid. Heartburn occurs when acid goes up the esophagus. Antacids are a base that causes a neutralization reaction with the excess acid in your body. So take Tums for your tummy.

Everything You Ever Wanted to Know About Turkey Osmosis—But Were Too Stuffed to Ask

A cold, salty bath for hours before cooking a turkey will draw fluid out of the turkey because the concentration of salt is higher outside of the turkey meat than inside. You might think this would dry it out—and in fact it does for the first few hours; but over time the turkey meat starts to pick up salt because osmosis works both ways. Therefore the salt increases the water-holding capacity of the proteins inside the turkey, so the flow of moisture actually reverses and the turkey starts to pick up water.

Groovy Gravy

All the fat from the drippings in your turkey pan is now in a pot. All that’s left to do is thicken the golden juices to make gravy. The recipe calls for flour or cornstarch as the thickening agent. OK…

Both flour and cornstarch use the carbohydrate starch to thicken sauces. Mixed with cold liquid, starch isn’t too thrilling—but add a little heat to the mix and the individual starch granules get to work, absorbing liquid and swelling.

By the time the mixture nears boiling, the starch granules will have grown to about ten times their size at room temperature. These swollen starch granules form a thick but tender matrix for the flavorful turkey drippings in your gravy, which thickens even more as it cools.

Although both flour and cornstarch owe their thickening powers to starch, cornstarch is pure starch, while flour contains starch plus protein.

What difference does a little protein make? Protein takes up volume but contributes little to the thickening power of flour. As such, you need about twice as much flour as cornstarch to thicken a sauce. That means flour is more likely to add an undesirable pasty flavor. While pure starch becomes transparent as it swells with liquid, the protein in flour reflects light, making a sauce look cloudy. Cloudy, velvet-textured gravy can be delicious, but cornstarch is used more often to thicken fruit pie fillings, creating a gemlike transparency around the fruit.

How Does a Pop-Up Timer Work?

Fun fact: it’s a pop-up stick and spring, held in place with a piece of metal solder. As the turkey cooks, the solder melts at 185 degrees Fahrenheit, and the pop-up stick is released. The solder melts at the same temperature at which the turkey is done. 

I don’t know about you, but this article is making us hungry. Whether you’re brining a turkey, trippin’ over tryptophan, or just plain stuffed silly, there’s a ton of chemistry at work in one of the best holidays ever.

At Wards’s, we hope you and your students have a lovely holiday with your families. Happy Thanksgiving!

As always, if you have any questions about chemistry or anything else, just ask the Ward’s Science Plus Us team at sciencehelp@vwr.com. Our in-house scientists and technicians are ready to answer even the toughest inquiries.