Q&A: Pia Sörensen and David Weitz on physics in the kitchen

Eleven years ago, Harvard University scientists Michael Brenner, Pia Sörensen, and David Weitz—with help from celebrity chef Ferran Adrià —created an undergraduate course on science and cooking. It was an instant success, and it spawned both an online edX course for mass audiences and a series of popular public lectures . After teaching the course for more than a decade, the three researchers decided to distill its contents into a new book, titled Science and Cooking: Physics Meets Food, from Homemade to Haute Cuisine, that is part popular science and part cookbook. In Physics Today‘s April 2021 issue, physicist Rama Bansil calls it an “entertaining introduction to the fascinating science behind gastronomy.” Sörensen and Weitz recently sat down with Physics Today to discuss the story behind the pioneering class and some of the far-out recipes featured in the book.

PT: How did the science and cooking class come about?

WEITZ: We had a postdoc from Barcelona who worked for Michael Brenner. He came to me and asked if he could invite the chef Ferran Adrià to come give a talk about science and cooking. At the time I didn’t know who Ferran was, but the postdoc told me he was the best chef in the world.

So I wrote a letter, and three days later Ferran said he was coming. We had him do a public lecture. And this was more than 10 years ago, so social media was not as predominant. But the Boston Globe had published an article about him the week before, so at the talk he was a rock star.

Ferran and I talked afterward, and we realized that I wanted to teach people a topic with broader appeal and he wanted to teach chefs about science. So we thought we could do a class, and then Michael Brenner came along, and he proposed the format we adopted. A couple of postdocs also helped formulate the basic idea of the class.

SÖRENSEN: It coincided with the launch of the new general education program at Harvard, which is supposed to connect what you learn in the classroom to the outside world. It just seemed like perfect synergy to bring it all together in the course.

WEITZ: It turned out to be amazingly popular.

PT: Most academics don’t know star chefs. Did you develop connections with other chefs after you met Ferran?

WEITZ: The first year, Ferran chose most of the chefs. But it turns out that most chefs want to lecture at Harvard if they’re given the opportunity. Now we just look in the press, and if we see somebody interesting, we invite them. Most people have heard of the class now and are willing to participate.

Times have also changed over the last 11 years, and we’re now much more aware of the importance of selecting a diverse group of chefs for the class.

SÖRENSEN: The food world has changed. When the course started, there was a lot of hype around molecular gastronomy and using the latest technology in the kitchen. Now there is more emphasis on local food, sustainability, and how chefs can influence the food system.

More recently there have been the issues raised during the pandemic—namely, an increased emphasis on diversity. I think our chef selection over the years has mirrored that development. But when we cook in our kitchens, the underlying science is what’s important. Recipes are not accidents. And the same is true when cutting-edge chefs create new things.

WEITZ: There’s more recognition now of cultural aspects. Food is culture, cooking is culture, science is culture—it’s all part of what we do.

PT: Were you passionate home chefs before you started the course? Or have you gotten into cooking because of the course?

SÖRENSEN: I always liked food, and I grew up in a home environment centered on food, cooking, and agriculture. But my passion for it came through teaching—I recognized what a fantastic teaching tool cooking can be. You get people thinking about food, and suddenly they start to ask scientific questions.

I have spent many years thinking about the molecular basis of the world. I used to do it in the context of cancer research, and now I do it in the context of food—they’re not so different.

WEITZ: I’m incompetent in the kitchen—I can make a cup of coffee, and that’s it. But I’m passionate about teaching science. How could I possibly cook when we have the world’s best chefs doing it? My role is to do the science.

SÖRENSEN: So often in universities, we learn from the experts in various fields. And for some reason, chefs have often been left out of that collaboration. But the chefs that have come to the class are at the forefront of their field, and they’re thinking rigorously about how to innovate in ways that I think resonate with a lot of different fields. It’s the first class in which creativity in cuisine really comes out.

PT: Is cooking more physics or chemistry?

WEITZ: I don’t distinguish between chemistry and physics in the kitchen—cooking is interdisciplinary. Soft-condensed-matter physics, which is what we call it, involves a lot of chemistry. On the physical side of things are the texture and its macroscopic behavior. Why does a gel behave like a gel, for example? How does all that work?

SÖRENSEN: When we cook, we change the texture and flavor of foods. Both of those are related to physics and chemistry, and both are related to biology in how we detect those flavor molecules in our mouths.

PT: Is there any moment during your time teaching the science and cooking course that is a particular favorite?

WEITZ: Teaching a class where kids actually want to come and listen to you!

SÖRENSEN: We had a chef two years ago from Singapore named Janice Wong . She likes to call herself an imagineer, and she makes edible chocolate paint in different colors. She had everyone collaborate on a large chocolate painting, so you’re experiencing the viscosity and watching as the chocolate crystallizes on your hands. Then we talked about the concepts—viscosity and elasticity. It was messy and beautiful.

PT: When did you get the idea to turn the class into a book?

SÖRENSEN: There was a lot of excitement from the public lectures and the online class, and it was a natural next step to capture that excitement in a book. It’s the culmination of 10 years of work. And it’s a collection of some of the most creative recipes and chefs of our time. But it also includes everyday recipes, like chocolate chip cookies and sauerkraut. All of those recipes are used to explain the science.

PT: What was your writing process like?

SÖRENSEN: We wrote pieces here and there. The hardest part was writing the first chapter. In a college class, students understand that they have to listen to us, but a reader can put the book down at any time. So how do you make engaging the concepts necessary to introduce the general ideas? That was a struggle.

PT: In the book, there are quite a few recipes that are more exotic than those you might find in a traditional cookbook. How did you learn about recipes like “old book essence”?

SÖRENSEN: Every chef who has a recipe in the book has been a speaker in the class, so we know them. We asked all of them for a recipe to include in the book. The old book recipe from Jordi Roca embodies the idea that you can take the essence from an old tome. It brings to mind the whole idea of Marcel Proust eating a madeleine and how flavor connects him to his memories. The recipe is centered on the idea of taking that old book flavor and putting it into a dessert.

WEITZ: If you knew Jordi’s personality, it would make total sense. He’s just got a crazy, wonderful personality and sees a kind of humor in things.

SÖRENSEN: I might not cook some of those recipes myself, but I enjoy admiring the lengths to which some go to create a beautiful piece of food meant to engage with your senses, your expectations, and your associations. It’s pretty cool!

PT: Can you recommend a classic recipe from the book?

SÖRENSEN: Molten chocolate cake —I feel like everyone should make it and think about the idea that molecules or heat diffuse into food. Cooking the molten chocolate cake batter also causes protein denaturation, as the proteins in the batter (from the egg) denature. You can see the effects of those microscopic changes with the naked eye.

PT: How about a more challenging recipe for experienced home chefs interested in haute cuisine?

SÖRENSEN: I really like Corey Lee ‘s thousand-year-old quail egg. It’s something most people probably haven’t made, and it challenges the notion of what cooking means. It involves ingredients that you would never think of—like lye and zinc. The scientific concept is the diffusion of these molecules into the egg, which takes a long time. That’s why you store the eggs in a brine solution for two weeks. The recipe also involves things on the side that seem delicious, like potage, cabbage juice, and pickled ginger. It has all the trappings of a fancy recipe in that it has many parts, but the science is there too.

PT: Do you have any graduates of the course that are now professional chefs?

SÖRENSEN: One student, Nick DiGiovanni, took the class his freshman year, went on to develop a special major in food, and then worked in Corey Lee’s restaurant in San Francisco. Senior year, he was taking another class with me on fermentation, and he disappeared halfway through the class. It turns out he was on Master Chef and was one of three finalists. Now he’s the biggest food influencer on TikTok and has 5 million followers.