Cooking as Practical Science


While enjoying the warmth of a fireplace, Harvard’s Richard Wrangham, Professor of Anthropology, came up with the idea that cooking may be what separates human beings from their evolutionary forebears.

In his book Catching Fire: How Cooking Made Us Human, Wrangham surmises that putting raw animal flesh to the flames before digging in made digestion far easier for early man. Consequently, the increasing ability to obtain more and more diverse calories led to our bigger and more developed brains.

Whatever the source of humanity’s IQ bump, cooking has certainly evolved—from a trial-by-fire affair to a sophisticated art. Creative chefs have played an essential role in the elevation of food, of course, but so have those wearing a different sort of white coat: scientists.

The invention of baking powder, essential for flaky biscuits, happened in a Harvard-affiliated facility rather than a kitchen. Moreover, some food items have become experimental classics. Edgerton’s milk-drop coronet and seemingly simple substances such as honey and cornstarch have helped scientists understand complex phenomena, from fluid dynamics to geological formations.

In fact, today’s molecular cooking techniques (also known as molecular gastronomy) rely on the same methods and even the same equipment found in the lab.

The resulting menus of bacon foam or flash-frozen hot chocolate have struck many as pretentious or just plain weird.

Looked at another way, these chef-scientists are drawing from the 19th century definition of their profession: Cooking as practical science. Whether or not we ate our way to evolutionary dominance, from that first crackle of fat on the fire to today’s dollop of culinary foam, the art and science of cooking have kept evolving, each ingredient complementing the other.

Culinary Q&A

Ferran Adrià’s December 12, 2008, campus visit was no mere flash in the pan.

By the tenets of a memorandum of understanding between SEAS and his nonprofit foundation, he will work with faculty and students, including David Weitz, to create a future academic course on molecular cooking.

Adrià offers patrons a taste of the unusual through the use of hydrocolloids, or “gums” that enable a delicate fruit puree to be transformed into a dense gel and relies on deconstruction techniques such as sterificacion, creating a resistant skin of liquid (as in a pea soup held in a pod of nothing more than itself).

Inspired by the famed chef's visit and the annual holiday lecture dedicated to the science of chocolate, we asked SEAS-based researchers and collaborators to pose and answer questions related to “experimental” food. Recipes (theoretical and practical) follow. Bon appétit!

Why does honey coil? (and other kitchen mysteries)

Honey on toast: L. Mahadevan’s quest to explore the inner workings of everyday experiences began with such a breakfast. In 1998, the recently hired assistant professor at MIT revealed a scaling law that predicted the coiling frequency of honey when poured from a particular height.

In addition to making playing with one’s food sound productive, Mahadevan’s elegant mathematics solved a longstanding conundrum in fluid dynamics that seemed nearly impossible to solve.

Curiosity might have driven the research, but he hinted at the more practical implications in a New York Times article that appeared soon after the finding, saying, “The geological flow of tectonic plates—the mechanism that creates mountain ranges—may be similar in principle to the flow of sheets of honey. We’ll have to see how it pans out.”

11 years later, a related finding did in fact pan out—curiously enough, with the aid of another pantry staple: cornstarch. Mahadevan helped colleagues at the University of Toronto solve the geological mystery of the Giant’s Causeway, an area on the coast of Ireland composed of 40,000 interlocking basalt columns resulting from a volcanic eruption. The crack patterns on drying samples of cornstarch are geometrically similar to the unusually beautiful stone pillars. This bit of supermarket science led to a quantitative explanation of how such complicated patterns arose.

One more tidbit too delicious to pass up: Mahadevan has made another classic contribution to kitchen science. He figured out why Cheerios tend to clump together or stick to the wall in a breakfast bowl of milk. The “Cheerio
effect” is due to the surface tension between the milk and the air.

The air/milk interface does not like to be deformed, but at the same time, gravity is pulling on the individual Cheerios. The two effects cancel, resulting in oatey holes that like to stick together. You may never look at breakfast the same way again.

Why does chocolate have sheen and snap when you break it?

Amy Rowat, a postdoctoral student in the Weitz lab, recommends not losing your temper when dealing with chocolate—perhaps one of the most scientifically complex foods you will ever encounter.

Chocolate is an emulsion of cocoa and sugar particles suspended in a continuous phase of fat. The natural fat of the cocoa bean (called cocoa butter) gives chocolate that sumptuous texture as it melts in your mouth. In addition, the fat is responsible for the candy’s characteristic glossy finish, homogeneous texture that snaps when you break it, and shelf life.

To make a solid bar, a chocolatier starts by melting chocolate and then letting it solidify into different shapes in molds. While cooling, the cocoa butter molecules transition from a liquid into a solid phase.

The molecules can crystallize into six different forms, each with a distinct phase transition temperature and material properties. Under the wrapper lie two crystalline forms, Type V and VI, that pack the molecules into a dense crystalline array. To achieve this uniform crystal structure requires a process called tempering (see sidebar).

A chocolatier cycles the temperature around the melting temperature to “melt out” the undesirable forms of crystals. The remaining mass of Type V seed crystals serves as nucleation sites for crystal growth, ensuring that the correct crystalline form dominates as the chocolate cools completely.

“As an everyday example, consider the soft graphite in a pencil versus a hard diamond,” says Rowat. “These materials both consist of carbon atoms but have vastly different mechanical properties, depending on the way the carbon atoms pack together.”

The process of tempering also helps explain why chocolate stored at the wrong temperature ends up looking dusty and moldy and crumbles instead of snaps when broken. The stable crystal forms melt, and upon uncontrolled cooling, nonuniform types of crystals form that do not pack together as densely.

“Different types of fat have different melting or phase transition temperatures, depending on the structure of the lipid molecules that make up the fat,” Rowat adds. “For example, olive oil is liquid at room temperature, while lard is solid. Understanding the composition of fat in chocolate also helps to explain why chocolate typically melts in your mouth, not in your hand. Above 97°F all crystalline forms of cocoa butter are liquid.”

How might aerosol science change the way we eat?

David Edwards is asking people to breathe what they eat. Along with current and former Harvard undergraduate students, including Trevor Martin ’10, Jonathan Kamler ’07, Larissa Zhou ’10, and chef Thierry Marx, he has helped commercialize what may become the newest olfactory sensation: Le Whif.

Dispensing with forks and knives, the technique encapsulates flavors in a compact aerosol delivery system (which looks like a large tube of lipstick), allowing the calorie conscious to “whiff” flavors such as chocolate.

When a whiff is inhaled, a cloud of tiny flavor particles suspended in a gas “coats your mouth,” creating a flavor sensation worthy of Willy Wonka.

The recently commercialized invention was sold in Paris starting in April and then taken on the road to various cities across the United States.

Aerosols have played an equally critical role in Edwards’ bioengineering research. While working in a food science lab, he came upon the idea of using a spray drying process to produce a new, more stable, and potentially more effective way to deliver TB vaccines.

Why is a creating a consommé so special?

“The clarification of a consommé is such wonderful biochemistry,” says Roberto Kolter, Professor of Microbiology and Molecular Genetics at Harvard Medical School and FAS. “You might as well be doing a precipitation of a protein [removing contaminants], since you are using the exact same techniques you would use in the lab.”

To create a consommé, a rich, intense broth that is at the same time delicate and nearly translucent, you start with a standard soup or stock. What keeps a thick soup thick is the suspension of proteins that are not quite in solution.

Thinning the soup without losing the flavor involves denaturation, a process in which proteins lose and change their structure, as when you fry an egg.

By adding egg whites (a water-soluble denatured protein) to a thick soup, “you create networks of denatured proteins that, as they are coming out of solution, trap all the other stuff not in solution like a molecular mesh,” says Kolter. In the process, any impurities in solution get trapped and eventually form into a gel-like scum (called raft) that rises to the top of the soup

Once the raft is filtered off, all that remains is in-solution, delightfully crystalclear liquid full of flavor. “You are taking something very cloudy—lots of stuff simply suspended but not dissolved— and taking away everything that is not in solution,” explains Kolter.

Clarification also plays a role in beverages such as beer and wine. For the refreshing taste of a pilsner, brewers rely on the flocculation (close gathering) of strains of yeast. Once strains that are just touching adhere, they settle, resulting in clarity.

Settling happens in winemaking as well, but the slower process of winemaking does not require such rapid flocculation. Kolter, a native speaker of Spanish, served as the chief translator during Adrià’s visit and had no qualms in inviting the famed chef over for dinner. “The reason why someone who loves to do biochemistry also loves to cook is because much of the tinkering you do at the bench top” is the same that you would do at the kitchen counter. Meaning, he felt right at home.