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
[Photos: Rachel Leah Blumenthal]
Over the course of fourteen lectures, the Harvard Science & Cooking series has touched on everything from the inner workings of meat glue to the exploration of deceptively simple questions like "What is fruit?" Last night marked the end of the season, and the lecture, titled "The Accidental Chemist," helped ground three months of occasionally abstract talks by coming back to the reason most of the audience was there: How can science help the home cook?
The final speakers hailed from America's Test Kitchen, headquartered just across the river in Brookline. Jack Bishop is the editorial director of Cook's Illustrated and Dan Souza is a senior editor, and they both worked on The Science of Good Cooking, an essential cookbook-meets-textbook released last year. "We analyze recipes," said Bishop. "Why do they work, and why do they fail?" The book, he said, represents twenty years of collective learning of the Cook's Illustrated team, aimed at elucidating science in the modern home kitchen. Many of the concepts discussed in last night's lecture can be explored in more detail in the book.
"We analyze recipes," said Bishop. "Why do they work, and why do they fail?"
According to Bishop, in a professional kitchen, innovation equals success. Given two equally well-prepared dishes, the one with a surprise will trump the classic dish every time. This is a departure from the restaurant world of three or four decades ago, when it was in fashion to create consistent replications of traditional cuisine. But in the home kitchen, the latter still holds true. Replication equals success.
Skills have degraded, though, and the typical modern home cook tends to have less intuition for replicating dishes. Our grandmothers cooked from a repertoire of the same forty dishes every night for decades, while we cook less often, jumping from one recipe to the next without repeating them, trying random things we find on the internet ("Good luck! That's probably not gonna work," said Bishop.) So, how can we improve? "Some application of science will help meet this goal of replication," said Bishop.
In cooking, there are countless sources of variability, and all of them can alter results or cause complete failure. One of the biggest potential problems is oven temperature inaccuracy. As an example, fourteen Cook's Illustrated employees went home and pre-heated their ovens to 350 degrees Fahrenheit, and the spread of actual measured temperatures covered a range of almost 100 degrees. Failures also frequently stem from the variability in our measuring techniques and skills. Eighteen Cook's Illustrated employees measured a cup of flour using the "dip-and-sweep" method, and there was a 13% variation amongst the measurements — and these are people who have been trained to measure properly. The best bet is to measure by weight instead of volume.
In cooking, there are countless sources of variability.
Some sources of variability are easier to control than others, but home cooks who arm themselves with some basic chemistry knowledge have the best shot at averting kitchen disasters. Bishop and Souza began with chemical reactions. What parts of the cooking process trigger a chemical reaction? They proceeded to explore three: mechanical force, heat, and combining ingredients.
One major example of applying mechanical force in cooking is using a knife, and Souza and Bishop turn to garlic and onions to explain. When whole, neither has much of an aroma, so where does the pungent smell we know come from? Cutting into them breaks the cell wall, allowing chemical reactions between amino acids in the interior of the garlic or onion and enzymes stored in the now-broken wall. In garlic, the enzyme in question is called alliinase, and when it interacts with a sulfur-containing amino acid from the interior of the clove, a compound called allicin is formed; it has a strong taste and smell, but heat converts it to mellower compounds. In onions, a different sulfur-containing amino acid reacts with alliinase to create thiosulfinates, compounds similar to allicin, which also convert to less pungent compounds when cooked.
The key here is that understanding the process can inform how we cut garlic and onions, and we have some control over the amount of these compounds that are created, ultimately determining the strength of the flavor. Slicing garlic thinly will yield a more mild flavor, while mincing it up finely, really getting that reaction going, will produce a much stronger flavor (which, of course, is desirable in some but not all recipes). Slicing onions through the root end gives the mildest flavor, while "manhandling" them in a food processor releases the most thiosulfinates, giving the strongest flavor. (Hint from Souza and Bishop: If applying for a job at America's Test Kitchen, do not use a food processor when asked to chop onions on a bench test. You will not get the job.)
"Either your knife skills or your knife needs an upgrade."
To illustrate the relationship between cell wall damage and thiosulfinate production in onions, Souza used potatoes. Thiosulfinate is known to have anti-oxidation properties, and oxidation is the reason potatoes turn black when peeled and exposed to air. Souza brought out three samples of "potato juice" (pureed and strained potatoes): one was just potato juice, one had hand-chopped onions added, and one had food processor-minced onions added. The potato juice alone turned virtually black due to oxidation when left in a refrigerator overnight, the sample with chopped onions looked light brown and smelled strongly of onions, and the sample with the minced onions showed barely any oxidation and smelled even stronger. If your cutting board is very wet when you're done chopping onions, or, similarly, if it's stained green after chopping herbs, you've damaged a lot of cells, and "either your knife skills or your knife needs an upgrade," said Bishop. Try sharpening the knife.
Another way to start a chemical reaction is to use heat. Souza and Bishop demonstrated with the example of "the incredible shrinking apple." The problem: You make a deep-dish pie with a beautiful, high crust, but you cut into it and find a huge gap between the apples and the top crust. The apples cooked down while the pie was baking. Additionally, the many apples required for the pie can yield a soupy filling and a soggy crust. But pre-cooking the apples actually solves all of these problems. The key is to cook the apples (and seasonings) gently, below 140 degrees Fahrenheit, and preferably in a covered Dutch oven before putting them in the pie. This slow, low heat causes the pectins — sugar-based compounds in the apple's cell wall — to convert to a more stable form that will protect the apples from getting too soft when they are cooked again in the pie. Described as "persistent firmness" by Harold McGee in On Food and Cooking: The Science and Lore of the Kitchen, this state can also be achieved by pre-cooking some fruits and vegetables, including as potatoes, sweet potatoes, and carrots.
The process works because these fruits and vegetables have an enzyme present in their cell walls that is active around 120 degrees Fahrenheit, reacting with pectin to make the pectin more amenable to being cross-linked by calcium ions, firming up the structure of the fruit or vegetable. (The calcium ions are being leaked out of cells as heat damages the membranes.) Heating slowly and gently, starting with the fruit or vegetable in cold water, allows the process to firm up the outside before the inside gets too mushy.
Souza and Bishop also explored one more way of creating a chemical reaction—one of the most basic actions of cooking, combining ingredients. To demonstrate, they provided insight into why some marinades ("mari-nahds," pronounced Bishop elegantly) work where others fail. The two takeaways: Salt is the key to a good marinade that actually penetrates the surface of the meat (most marinade components remain on the surface and can't actually make meat tender), and acid-based marinades can make meat dry and tough and should only be used for an hour or less.
The Cook's Illustrated folks are so enthusiastic about the wonders of salty marinades that they've dubbed them "brinerades."
The Cook's Illustrated folks are so enthusiastic about the wonders of salty marinades that they've dubbed them "brinerades." The salt serves four purposes: restructuring the meat's proteins to make more room for juicy pockets of water and to loosen fiber bundles, increasing tenderness; dissolving some proteins, creating even more room for moisture; seasoning the meat; and bringing even more moisture into the meat by triggering osmosis, where the water moves from an area of higher concentration (the marinade) to an area of lower concentration (the meat). Most other flavor-imparting marinade components, like herbs and spices, can't actually get far into the meat, because they're fat-soluble rather than water-soluble; the water in the meat repels them. Including an oil in the marinade at least helps these ingredients cling to the surface of the meal. Onions and garlic, however, are water soluble, so they can help flavor the meat.
As for acids, it's a common misconception that they can tenderize meat well. In fact, they can make meat mushy at the surface—they do break down muscle fibers and collagen, but they can't penetrate far beyond the surface, and if left on too long, they'll cause mushiness without increasing tenderness. Worse, they can actually make meat drier. At a somewhat acidic pH level of 5.2, all muscle proteins are at their isoelectric point, where there are equal numbers of positive and negative charges. This state of balance makes the proteins pack closer together, which eliminates space for moisture. Take chicken, for example, which is already slightly acidic, around a 6.0-6.5 pH level. Adding an acidic marinade can take that number down far enough to hit the isoelectric point, and then it's goodbye juiciness. So, the lesson in marinades: salt is important. Acid isn't necessarily a good thing. If you want to use acidic ingredients like wine or yogurt, make it quick.
The team found that an omelet cooked without butter was tough enough to hold up a two-pound weight.
In addition to exploring three types of chemical reactions, Souza and Bishop provided several case studies to explore a few other scientific concepts that pop up in the kitchen. One useful lesson is that fat has a protective effect on the coagulation of eggs, so incorporating butter into an omelet, for example, will yield tender, fluffy results. In the test kitchen, the team found that an omelet cooked without butter was tough enough to hold up a two-pound weight, while the buttery omelet was appropriately soft and got crushed by the weight. When eggs are cooked without fat, the protein strands quickly bind together into a tough, cross-linked structure, squeezing out moisture, but fat helps coat the proteins, slowing down the process so the eggs aren't yet tough when they're done cooking.
Another lesson: let bread rest before kneading in order to require less kneading. This saves time and also helps prevent bad results from kneading too much, which is easy to do in the age of stand mixers. The technique of allowing a resting period is called autolyse. First, the flour and water are mixed together, which gives the flour proteins, glutenin and gliadin, the chance to start organizing themselves into a matrix of gluten. But at this stage, the matrix is still fairly disorganized and tangled; kneading will sort everything out with time. Allowing a rest period first gives the partially formed matrix a chance to break back down into smaller bits that will align much more quickly and easily when kneading begins.
Science isn't something to be feared in the kitchen.
In the end, it all comes back to the point driven home by many of the other lecturers throughout the season. Science isn't something to be feared in the kitchen. Understanding basic chemistry can help home cooks make good decisions and gain a greater intuition for how to make adjustments throughout the cooking process. "In our day, people don't know enough about science," said Bill Yosses, the White House pastry chef, earlier in the series. "Without an understanding of science, we don't make intelligent decisions."
Several weeks later, Wylie Dufresne of wd~50 made a similar point: "There will never be a right or wrong way to cook something," he said. "But there will always be a more informed way." Applying science in the kitchen doesn't necessarily mean creating "meat glue" or spheres or foams. Sometimes it's as simple as understanding why your yogurt-based overnight marinade yielded tough lamb chops, and what you can do to fix it.
— Rachel Leah Blumenthal