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Joanne Chang's Harvard Lecture: 'The Science of Sweets'

Harvard University's third annual Science & Cooking public lecture series brings chefs from around the world to lecture on the intersection of science and cooking. And Eater Boston editor Rachel Leah Blumenthal is on the scene. This week: Joanne Chang of Boston's Flour Bakery + Cafe and Myers + Chang.

[Photos: Rachel Leah Blumenthal]

Last night's installment of Harvard's Science and Lecture series brought in a chef from closer to home than previous lectures: Joanne Chang owns Flour Bakery + Cafe, with three Boston locations and one in Cambridge, as well as Myers + Chang, an Asian-inspired "funky indie diner" in Boston's South End. Her lecture title, "The Science of Sweet," came from the name of a television pilot she was told that she was filming a few years back. After hours of research and preparation and a day shooting the supposed pilot, she was surprised on day two by a visit from Bobby Flay. He was secretly filming her for his show Throwdown With Bobby Flay and The Science of Sweets was all a cover up. She looked bewildered in the television clip, and at the lecture, she confessed that she was disappointed she didn't get to actually make a science show. (As for the throwdown, Chang's renowned sticky buns won out over Flay's attempt.)

The science behind the wide world of sweets — or the slightly narrower world of Flour's sweets — would take months or even years to really teach, Chang said. Instead, she focused on four basic types of baked goods, discussing some of the scientific workings behind each one and some common problems that bakers encounter.

The baked goods in question: bread, pie (just the crust), cream puffs, and cake. All start from nearly the same group of ingredients, Chang explained. But by manipulating proportions, temperature, time, and other factors, different pastries emerge.

Chang discussed bread first; in terms of ingredients, it's perhaps the simplest. It can be made with flour and water alone, although yeast and salt are useful additions for rising and flavor, respectively. For the purpose of the lecture, Chang focused solely on wheat flour, which comes in different types — cake, all-purpose, and bread, for example. The difference between them is the amount of gluten (or rather, gluten's components), with cake flour having the least and bread flour having the most. Those components are two of wheat flour's proteins, gliadin and glutenin, which coexist without interacting very much until a liquid is introduced. Then, they are bound together into gluten, a protein composite that takes the form of an elastic web-like structure.

To illustrate the difference in gluten content between cake flour and bread flour, Chang used the example of a soap bubble versus a balloon. A bubble traps some air inside of it, but it's ephemeral, while the balloon more sturdily traps and holds air. (All-purpose flour is in the middle of the range, and as its name suggests, it's suitable for cakes, breads, and everything in between.)

Like a balloon, bread dough traps a lot of air pretty firmly in its gluten web. Kneading helps the process along as it better combines the flour and water, creating more gluten bonds. While this is sufficient to make bread rise (the air expands as it heats in the oven), the addition of yeast boosts the process by adding even more air.


Since yeast is a living organism, it's typically sold dehydrated and thus "unconscious." When added to the flour and water, it wakes up (due to the rehydration) and finds itself surrounded by food. After eating, it does what humans do: it expels gas. "It burps and farts," said Chang. The gassy activity of the yeast causes the dough to rise even before it goes into the oven. Then, once the dough starts heating up in the oven, the yeast "have one last hurrah" and "go on a feeding frenzy" because they know death is imminent, explained Chang. More burping and farting contributes to the "oven spring," the continued rising of the dough. The evaporation of water also contributes, as the resulting steam can be well over 1000 times the volume of the water. And the air trapped in the gluten web can expand two to three times when heated as well.

The example of bread also gave Chang the opportunity to touch on the Maillard reaction, which causes browning of things like meats and bread crust. In short, at a certain temperature, an amino acid interacts with a sugar, and the reaction results in a change of color (browning) and taste. Caramelization results in similar visual and flavor changes but is not actually an example of the Maillard reaction.

Chang asked the audience what problems they've encountered baking bread, and the main issue was that it didn't rise. A few possible causes: the yeast was already dead (maybe it was stored for too long before use), the gluten web wasn't fully created (not enough kneading), or the oven temperature was too low.

Basic pie crust is also made from flour, water, and salt, but the yeast is replaced with butter. The goal with pie crust is the opposite of bread — it's important to prevent gluten from forming. Instead of mixing the flour and water, a baker adds butter to the flour first. The fat coats the gliadin and glutenin, preventing them from bonding into gluten once the liquid is added. Bakers should also take care to leave chunks of butter in the mix in order to create a flaky crust. The dough is ready when it can be clenched and keep its shape, but go too far, and you get cookie dough. Don't coat enough flour with fat, and the crust will be too tough. "A lot of baking is patience," said Chang. Timing is everything.

In a step called "frissage," a baker smears pie dough out with her palm, forming sheets of butter out of those chunks that were left intact. This is where the flakes come from, and a non-flaky crust could be due to the sheets not being long enough.

Once the dough is in the oven, it rises a little bit due to the evaporation of water into steam, but it doesn't rise nearly as much as bread since it's lacking that air-trapping gluten web or any leavening agents.

Cream puffs are also made with flour, water, and butter, but eggs are added to the mix, as well as sugar and salt (just for flavor). The process begins with the addition of melted butter into water; it's melted so that it will disperse amongst the water, forming an emulsion. This allows some gluten formation but also prevents some. The eggs serve a few purposes. The whites add both liquid and structure, while the yolks add lecithin, an emulsifier that helps keep the butter and water in place, since they normally wouldn't interact in that way. Last week's speaker, Nandu Jubany, spoke at length on lecithin.

When cream puffs go in the oven, evaporation of the liquids cause them to puff up. The gluten hardens to create a crispy crust, leaving a hollow inside where the liquids had been, which is perfect for the addition of a cream filling. For Christmas, Chang likes to create croquembouches, towers of cream puffs surrounded by a nest of spun sugar. She demonstrated the making of the nest, quickly spinning caramelizing sugar into threads and dropping them onto a ready-made tower of puffs. Advanced bakers will find that the sound of sugar caramelizing changes throughout the process; you can tell when the time is right to spin by listening closely and learning those sounds, she explained.


Cake builds on the previous examples: now, there's flour, butter, eggs, sugar (not just for flavor this time), a liquid (buttermilk, for example), and a chemical leavener such as baking soda. The first step is to cream the butter and sugar together. The eggs play the same roles as in cream puffs — liquid, structure, emulsifier.

Baking soda reacts with an acid in the cake (buttermilk, cocoa, lemon juice, or brown sugar, for example) to yield a light, fluffy texture. But if there are no suitable acidic ingredients, bakers can use baking powder instead of, or in addition to, baking soda. Baking powder is essentially a self-contained leavener made of baking soda and cream of tartar, a powdered acid culled from a byproduct of the winemaking process.

To test out the importance of the various ingredients in her basic yellow cake recipe, Chang and her bakers tested a number of variations. Using no leavening yielded a gummy, dense, and sour cake, for example, while cutting half the sugar was actually pretty good, giving Chang some ideas for the new cookbook she's currently working on, which focuses on low sugar and sugarless baking.

The most common audience cake complaint was that the middle of the cake sometimes sinks. This could be due to too much leavening, Chang explained. The cake pan is only a few inches high, so if the cake rises too much, it will eventually lose support on the sides and collapse in on itself. A too-cold oven can also cause sinking as the sides will finish baking first, leaving a potentially undercooked center.

The night ended with actual cake samples all around and a never-ending stream of audience questions, many more than the timid few at most other lectures in the series. Science applications in baking are perhaps the most accessible to a general crowd — or the mental image of yeast burping and farting was enough to loosen everyone up.

— Rachel Leah Blumenthal

The Harvard Science & Cooking lecture series continues on Monday, November 11th, with Wylie Dufresne (wd~50) and Ted Russin (The Culinary Institute of America) speaking about enzymes in the kitchen. Seating for the free event is first come, first served, and more details can be found on the Harvard website.

· All Joanne Chang Coverage on Eater [-E-]
· All Coverage of Harvard's Science & Cooking Lecture Series on Eater [-E-]