Understanding the Science of Thanksgiving

Ever wonder how those pop-up turkey thermometers work? Or how much turkey it takes to make you sleepy? Madeleine Brand speaks with Catholic University of America chemistry professor Diane Bunce about the science of Thanksgiving.

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MADELEINE BRAND, host:

Well, here in the US, we are all too familiar with overconsumption, especially today. But how many of us know about the science at work in our food and our stomachs? Well, I spoke earlier with Diane Bunce. She's a chemistry professor at Catholic University. She gave me the lowdown on the science behind Thanksgiving.

Tell us about tryptophan. Now I've heard conflicting stories about this; one, that too much tryptophan puts people into a deep doze, shall we say--too much turkey and too much tryptophan. But then I read the other day that that's a myth.

Professor DIANE BUNCE (Catholic University): Well, the story's a little more complicated. Tryptophan itself is the starting material for the body's manufacture of serotonin. Serotonin is what makes you sleepy. But when you eat a large dinner, like a Thanksgiving dinner, the tryptophan is interfered with by all the carbohydrates you eat. So usually you feel tired or sleepy after a large dinner because of the massive dose of carbohydrates. But if you came in late at night when your stomach was empty and you had a piece of turkey off that carcass in the refrigerator, then the tryptophan could contribute to the production of serotonin.

BRAND: Just one little piece of turkey?

Prof. BUNCE: Well, no, it would take a little bit more. Tryptophan is what's called an essential amino acid, which means it's an amino acid you must take in in your diet. Your body needs it but your body can't manufacture it.

BRAND: OK. Now let's talk about gravy. I'm terrible at making gravy because I don't understand how to make it thick with the cornstarch or the flour. Tell us about the chemical properties of that.

Prof. BUNCE: Well, it turns out that cornstarch vs. flour is the source of a lot of family arguments on Thanksgiving morning, especially between mothers and mother-in-laws of newly married couples. Flour is traditionally used in the United States because it's considered to be natural and it will thicken at a lower temperature, but it also makes your gravy more opaque. Cornstarch is modified starch. It's been processed. And all of the proteins that you would find in regular flour have been removed. So when it is used to thicken gravy, it makes a more translucent gravy.

BRAND: And tell us about the science of the pop-up thermometer in the turkey. How does that work?

Prof. BUNCE: Well, it seems like it would be something very complicated, but it's actually very simple. It's a little plastic plunger that's held down by a spring and it is held in the down position until the turkey's at the right temperature and then we all know it pops up. Well, what holds it in the down position is actually a little drop of solder, and when the turkey gets to 185 degrees Fahrenheit, which is the temperature at which poultry is considered to be done, the solder melts, the pop-up plunger moves up, and you know that your turkey is done.

BRAND: So there's liquid metal in your turkey?

Prof. BUNCE: Well, solder is a solid at cold temperatures and a liquid at--in this case, 185 degrees. It's encased in a double wall of plastic. But it is still metal.

BRAND: Let's move on to dessert, and I'd love you to address this--I don't know if it's a myth or not, but people say that if children eat too many sweets, they get hyperactive.

Prof. BUNCE: Well, there is some scientific basis for that, and that has to do with children reacting to high sugar content, but how much sugar, what the body weight of your child is, what your child's temperament is, how fast your child got just the sugar, these are all variables you have to take into account. If your child likes to eat a lot of dessert, you can take a small sliver of a lot of different types of pies and give them a variety instead of giving them large pieces of each different pie.

BRAND: Diane Bunce is a chemistry professor at Catholic University in Washington, DC, and thank you very much and have a very chemically wonderful Thanksgiving.

Prof. BUNCE: Thank you, and you do the same.

BRAND: I will.

DAY TO DAY is a production of NPR News with contributions from slate.com. Have a great Thanksgiving, everyone. I'm Madeleine Brand.

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