A chemical reaction gives Thanksgiving’s turkey its golden-brown color and roasted flavor.

Brent Hofacker/Alamy Stock Photo

How to science up your Thanksgiving dinner

Ever wondered how the Thanksgiving turkey gets its golden-brown color and rich roasted flavor? The answer is science. Chemical reactions and physical transformations are key to any dish, from mashed potatoes to pumpkin pie. That’s why many cooks and scientists get hooked on the science of food.

Take Dario Bressanini, a physical chemist at the University of Insubria in Como, Italy: He spends most of his day studying how positrons—the antimatter counterpart of electrons—interact with atoms and molecules. But in his free time, Bressanini turns into a food science nerd: His YouTube channel and monthly column and blog for Le Scienze magazine, the Italian edition of Scientific American, are all about the physics and chemistry of food. Bressanini has also published seven books, including one about the science behind pastrymaking, whose Spanish edition was released last month.

He chatted with Science about his passion for the science of food. This interview has been translated from Italian and edited for clarity and length.

Q: How did you get interested in food science?

A: In 1990, I was sent for 1 year to [the University of California,] Berkeley, for my Ph.D. training. Up to that moment, I had been living with my parents, so I didn’t know how to cook. Since the Berkeley cafeteria wasn’t great, and I couldn’t afford to go to the restaurants, my mom was mailing me her recipes. In my hands, they often didn’t work out, so I started asking myself questions and experimenting with food. Sometimes I could understand recipes and improve them by using simple chemistry or physics concepts. For example, I improved my Bolognese sauce by separately sautéing the greens—onion, celery, and carrot—and the meat. This trick speeds up a chemical reaction that browns the meat, which would be slowed down by the water in the vegetables.  

When I came back to Italy to teach thermodynamics at the University [of Insubria], I started using everyday life, especially cooking, to explain chemical reactions or physical phenomena to my students. This approach really helps them understand complex or abstract concepts. For example, I use melanzane alla Parmigiana [eggplant parmesan] to explain osmosis, the process during which solvents like water move through a semipermeable membrane from an area where solutes like salt are at lower concentration to an area where they are at higher concentration. The traditional Parmigiana recipe calls for kosher salt to be spread over the sliced eggplants to draw out excess water, before frying them: That’s osmosis at work.

Q: Why did you decide to start a blog about the science of food?

A: To me, the kitchen is a big laboratory. When I started writing for Le Scienze in 2005, I realized there wasn’t enough room in a standard article to explain my home experiments, so I started the blog. My posts help people repeat the food experiments at home, and learn about science and its methods, such as the importance of measuring ingredients and having a control to validate hypotheses. If people without a scientific background learn how the scientific method works, they can better understand research on issues such as vaccine safety and global warming. I also use my blog to talk about controversial topics, like genetically modified organisms, and debunk food myths.

Q: What are the most common food myths?

A: The ones about popular ingredients such as sugar or salt. Many think that the pink Himalayan salt is healthier than regular salt because it allegedly contains 84 nutrients, but no scientific evidence backs this up: Himalayan salt is at least 97% sodium chloride [table salt] plus mineral impurities such as iron, which give it a pink hue. Other people think brown sugar is better than white sugar because [brown sugar] is unrefined, so it still contains important minerals such as iron. That’s true, but these minerals are present in such little amounts that they can’t have any beneficial effect. Some others think white sugar is bad because it’s “whitened” with chemical substances, but that’s not true: Sucrose is naturally white. The idea that there’s a better sugar or salt is dangerous, because instead of reducing the intake of these substances, people will start replacing them with other sugars and salts, which are equally unhealthy.

Q: What’s the most common chemical reaction in our kitchens?

A: The Maillard reaction: We see it every time we toast marshmallows, bake cookies, or roast meat, fish, and vegetables. As we cook these foods at high heat and in the absence of water, the sugars and proteins naturally contained in them react together and form a mixture of molecules, which arrange themselves into microscopic structures that give food a brown hue when light bounces off them. Think about the golden-brown color of toasted bread or roast turkey. Depending on which sugar reacts with which amino acid, the Maillard reaction also produces a series of characteristic flavors—from malty to meaty—which we associate with roasted, grilled, and seared dishes. The Maillard reaction is what gives the onions on top of Thanksgiving’s green bean casserole their golden color, crispy texture, and slightly sweet flavor. 

Chemical reactions are also common in pastrymaking, where acid ingredients react with sodium bicarbonate [also known as baking soda] to produce carbon dioxide, which forms gas bubbles and helps doughs rise. That’s why baking powder, which is made of baking soda and a weak acid, is used to get fluffy cakes and quick breads such as cornbread.

Dario Bressanini at a barbecue competition

Dario Bressanini

Q: Can you tell us the science behind a popular dish?

A: The key to a perfect pulled pork is to use a cut of meat that comes from the upper part of the pig. This cut of pork has a lot of connective tissue that keeps together the muscle fibers. When the connective tissue melts, it turns into gelatin, a lubricant substance that keeps the meat tender. Also, because the muscle fibers are not kept together by the connective tissue anymore, they can be easily “pulled,” or broken into individual fibers. Another cut of meat that is not rich in connective tissue, such as the fillet, would result in a dry, stiff pork.

Q: What’s a science-based tweak on a traditional Thanksgiving dish?

A: I’ve found a way to get creamy mashed potatoes without using butter. The secret is cooking the potatoes twice. I first cook them with their skin at 75°C–80°C: This temperature activates an enzyme that separates individual potatoes’ cells without blowing them to pieces and breaking the starch granules within them. (If broken, starch granules become sticky and give the potatoes a gooey consistency.) Then, I let the potatoes cool down and cook them again at about 90°C to make them easy to digest. At high temperatures and in the presence of water, the starch granules lose their structure and can be easily degraded by our digestive enzymes. Finally, I delicately mash the potatoes with a fork—I never use a mixer as it would break the cells. The intact cells, which are free to flow one over the other, create a lubricant effect that mimics that of the butter fats.

Q: What aspect of food science is the most fun?

A: With science, one can invent new recipes. A few years ago, I came up with a meringuelike sweet that I dubbed “milky cloud.” Traditional meringues are made with sugar and beaten egg whites, which are rich in water and proteins. Since skimmed milk is made mainly of proteins, sugar, and water, I tried to use it to replace eggs in meringues—and it worked. A pastry chef who read my book on the science of pastrymaking decided to use these milk-based meringues for a new dessert.

Q: Have you ever thought about becoming a chef?

A: I’ve taken cooking and baking classes, but I wouldn’t want to become a professional cook. I enjoy being a scientist, though at some point I’d like to do some research on food science.

*Correction 23 November, 8:45 a.m.: This story has been updated to give a more accurate description of osmosis.