The Science Behind Thanksgiving Dinner

For many people in the U.S., Thanksgiving gatherings will look a bit different this year. While family and friends may be virtually sharing a meal instead of sitting around the same table, the Thanksgiving feast remains the main attraction. 

We connected with IFT member Kantha Shelke, PhD, CFS, to help us deconstruct the turkey day menu and dive into the science behind this flavorful day. Here’s what she had to say. 

Q: Why do all the Thanksgiving flavors go so well together?

Shelke: Ingredients in the typical Thanksgiving dinner have many flavor components in common. Root vegetables and members of the onion family share many similar flavor compounds. Roasted turkey and fried turkey have compounds in common with apples, chocolate, pumpkin, pecans, molasses, honey, parsley leaves, ham, tomatoes, and roasted vegetables. Since our sense of smell is responsible for 80 percent of the flavors we taste, the combination of tastes and aromas come together to create Thanksgiving flavors that complement each other well.

Q: What is the difference between organic, wild, free-range, and conventional turkeys?

Shelke: An organic turkey simply means that the bird has met the standards for USDA Organic certification, including an organic diet and surroundings such as bedding and grazing areas. It is also raised without hormones and steroids and has been processed without preservatives.

Wild turkeys are birds that were not domesticated or fed by humans—they’re essentially hunted for the meal. In contrast, free-range turkeys are birds that are not confined to a cage, but were allowed to roam and forage. Because their diets were augmented with grubs, worms, and grass, the flavor of their meat is distinctly flavorful, and the exercise supposedly improves the texture too.

Conventional turkeys are the classic turkeys in grocery stores that are available year-round called broad breasted white. They are selectively bred to put on maximal breast meat in minimum growing time.

Q: How big of a turkey should a person buy and how long before cooking it?

Shelke: The size of the turkey depends on how much you like leftovers. A general rule of thumb is a pound per person and a pound and half per person if you want something to nibble on after Thanksgiving. 

If you want a fresh turkey (which has never been chilled below 26 degrees Fahrenheit) for Thanksgiving, buy it on Tuesday so it is not stored for longer than two days in the refrigerator. This also applies for turkeys sold as defrosted and labeled as “previously frozen.” A frozen turkey may be bought any time and kept frozen until ready to thaw.

Q: How do you properly thaw a turkey and how long does it take? 

Shelke: If you are buying a frozen turkey, plan for 24 hours of refrigerator thawing time for every five pounds of turkey. For faster thawing, submerge the frozen turkey (still in its packaging) in cold water and change the water every 30 minutes. It takes about 30 minutes per pound to thaw in cold water.

Q: What does it mean to brine the turkey and why is it beneficial?

Shelke: Turkey is a lean bird and does not have enough fat to keep its meat—especially breast meat—moist and prevent it from becoming dry and tough. Brining is a simple technique of soaking the bird in a solution of salt and water to coax more moisture into the meat before it is cooked to keep it moist during cooking. Turkey may also be dry brined by rubbing a mixture of salt, seasonings, and/or sugar directly onto the meat and skin and refrigerating the turkey for a few hours before cooking. The salt and sugar, in addition to adding flavor to make the meat delicious and juicy, tenderize it by breaking down the protein fibers.

Q: What is the science behind the pop-up thermometer in the turkey, how does it work, and can it be trusted? 

Shelke: Turkey is done cooking and safe to consume when it reaches 165 degrees Fahrenheit. The pop-up timer, which often comes with the turkey you buy at the grocery store, tells you if the part it is stuck into is cooked or not cooked. While it is pretty reliable—within 1-2 degrees Fahrenheit—it is always a good idea to use a food thermometer and check the thicker parts of the turkey meat to ensure that it is indeed done. For a refresher on how to properly use a food thermometer, watch our Food Facts video.

Q: How does a starch help to thicken gravy? Is flour or cornstarch better?

Shelke: Commercial starch—such as cornstarch, tapioca or rice starch—is made of starch granules. These little particles don’t do much when mixed with cold water or any liquid 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 that thickens even more as it cools. 

Cornstarch is better than flour for thickening, because unlike flour which also contains protein and fiber, cornstarch is purely starch granules.

Q: How long does cranberry sauce keep in a can versus freshly made?

Shelke: Canned cranberry sauce can last for as long as two years in an unopened can because manufacturers make sure it has the perfect balance of acid and sugars for food safety. The absence of air in the can helps retain the flavors and the nutrients from getting oxidized, contaminated, or spoiled.

Freshly made cranberry sauce, on the other hand, will last for about a month in the refrigerator in a covered container.  Although cranberries are very acidic, the preparation involves the addition of sugar. It spoils more quickly than canned cranberry sauce because it is exposed to air and the environment repeatedly.

Q: Why do most people like pumpkin pie warm or at room temperature?

Shelke: People like pumpkin pie at room temperature, because at that temperature, the filling has the perfect creamy texture and the crust is still delightfully crunchy and flaky. People who enjoy warm pumpkin pie are seeking its aromas, and they relish the flavors in the filling and the buttery notes of the crust. In addition, warm pumpkin pie is the perfect contrast for an ice cream or whipped cream topping.

Q: What about Thanksgiving makes you sleepy— is it really L-tryptophan or overeating?

Shelke: Although the after-dinner stupor associated with Thanksgiving is often attributed to the turkey and its amino acid L-tryptophan, which has a documented sleep effect, even those who omit the turkey will complain about feeling sleepy after the feast. That’s because L-tryptophan is also present to the same extent in other protein foods such as pork, ham, chicken and cheese—about 0.3 grams per 100 grams of the food. Science has shown that L-tryptophan acts as a sleep inducer only when taken on an empty stomach. 

It is most likely that the quantity of carbohydrates and fats consumed during the meal redirects the blood to the digestive system and leaves one feeling sleepy, at least until they are revived by that additional slice of pie!

About Kantha Shelke, PhD, CFS

Kantha Shelke, PhD, CFS, is the founder and principal at Corvus Blue LLC, a food science and research firm, senior lecturer, food safety regulations at Johns Hopkins University, and a food science communicator for IFT. A diversified scientist, Kantha works at the intersection of food science and its application for health and wellness, focusing on the science of food processing, physiology, regulatory clearance, processing trends, commercialization, and the dynamics shaping acceptance and adherence by consumers and markets.