A Pinch of Culinary Science

by Anu Inkeri Hopia

  There are numerous books about additives, taking various perspectives and views. We will not go into the discussion for or against additives, except acknowledging that they are among the most thoroughly tested ingredients we eat. They are often necessary in order for our food to be safe, have the required texture and so forth, and many of them are even sourced directly from the world of plants with little processing. The famous food writer and documentarist Michael Pollan is often quoted on his statement, “Don’t eat anything your great-grandmother wouldn’t recognize as food.” However, in the case of the mock apple pie, it is indeed our great-grandmother who baked the pie based on flavors from additives rather than apples! Surely, there is no rule without a few exceptions. The fact that the participants at the workshop didn’t appear very skeptical to the mock apple pie might be because they were already well seasoned through participation in many such science-based food workshops, or they might have been familiar with chemistry and, therefore, accustomed to chemical language. If you wanted to convince an “additive skeptic” to eat the mock apple pie, perhaps the knowledge that it is cooked from an old “traditional” recipe would balance the feeling of risk and novelty and instill a notion that it is safe to eat? As a contrast to the additive skeptic, the French researcher Hervé This has, together with food professionals, spent much effort in developing dishes, and even whole meals, based solely on combinations and manipulation of pure chemical substances, that is, “note by note cooking.” That must be the ultimate way of cooking from scratch. When, or if, such foods are made available for a broader community, the producers will surely have to reflect upon which words they use in their ingredient lists.

  In addition to our knowledge of the ingredients’ names, the name of a dish might affect our perception of it. Researchers Line Holler Mielby and Michael Bom Frøst from the University of Copenhagen found that when (very fortunate) volunteers were served an avantgarde fine dining meal that included some “challenging” courses, the manner in which the waiter described the dish affected how the guests experienced the food. The guests gave a more positive evaluation of a course if the waiter presented it with descriptions of the ingredients and the procedure of cooking and assembling the dish. The same course was rated lower if it was presented accompanied by an artful name, or simply without any comment at all. This is something to reflect upon the next time you have someone for dinner that you expect will be skeptical about what you serve them. Indeed, language has great power over our experiences of food and drink!

  2

  Boiling an Egg from the Inside Out

  In 2006, we got our hands on a book we had waited for with great anticipation, written by the French professor Hervé This, a pioneer within molecular gastronomy since its very conception. The book, Molecular Gastronomy, published in French four years earlier, was finally available in English translation. On a side note, during our years of waiting, NASA had (in 2003–04) found time and resources to launch and land two rovers on the planet Mars. More on this later in the chapter. We were especially intrigued by what we read in a chapter about cooking eggs. It says: “At 62°C one of the proteins in the white (ovotransferrin) is cooked, but the yolk remains liquid because the proteins that coagulate first in this part of the egg require a temperature of 68°C. Obviously this would mean longer cooking times, but the result is a perfectly cooked egg” (see table with egg white proteins in the next chapter). So, the egg yolk and white contain their particular cocktails of proteins, coagulating at different temperatures. In everyday language this would mean that the egg white becomes solid at 62°C and the yolk solidifies at 68°C. Eureka! Imagine the classical hotel breakfast egg problem: you pick an egg from the basket promising soft-boiled eggs, but when you open the egg you realize it would have survived a round of boccia without taking too much damage. We had at last been served the solution to this dilemma. Fill a pot with water, make sure the temperature is between 62°C and 68°C, pop in a few eggs and wait. After a while, although longer than if the egg was cooked in boiling water, you would get a risk-free soft-boiled egg. This knowledge could change the way millions of eggs are cooked all over the world. Hotels could now guarantee perfect soft-boiled eggs from 7am until the breakfast buffet closes around 11am. The chefs can basically forget the cooking time, just make sure they have strict control over the temperature.

  To the lab! We didn’t waste much time and went straight to the lab next morning. We set up a thermostat-controlled water bath at exactly 65°C and popped in four eggs. But for how long should the eggs cook? We chose to be on the safe side and went to the office for the rest of the day, returning to the lab in the afternoon. Protein chemistry has taught us that each protein has its specific conditions, such as temperature and pH under which it denatures, its molecular shape being changed and finally coagulates into a solid substance. In the protein chemistry books there is usually no mention about reaction time however. Thus, two of the eggs were extracted after a short day’s work, and the remaining were left to cook until next day. As long as the temperature was held below 68°C, the yolk should not coagulate, right? Giving two eggs the same treatment would ensure us some measure of repeatability; at least, if the same thing happened with both eggs. In case they came out different, we’d know that we should repeat the experiment.

  Proteins are long molecules, composed of hundreds or thousands of amino acids linked together in a long chain, which is again bundled together in a specific way. The shapes of the bundles are affected in varying degrees during cooking. Subjected to either heat, physical stress (as in whisking egg whites), or in contact with acids, the bundles start unfolding. Denaturing is a mild structural change which is not always visible to the eye; the egg white is still translucent and the meat of a steak has not changed its color or texture markedly. Harsher treatment of the proteins will result in coagulation, a stronger and irreversible change in protein structure. The strings start reacting and hook up with each other to form a three-dimensional network. This is clearly visible to the naked eye: an egg white changes from translucent to opaque, meat or fish becomes firm, scrambled eggs become lumpy, milk curdles. ×

  The first two eggs were cracked open after six hours in the bath. There, on the plate, a whitish, slushy and rather liquid white poured out while the yolk rolled out in the shape of a soft ball. Not only one egg, but both. It seemed as if the eggs were cooked from the inside out! Next morning, 26 hours after they entered the 65°C water, the remaining two eggs were extracted. The observation was more or less the same as for the first two eggs, but the yolks were even more firm while the white was still not completely set. During the subsequent weeks and months, the experiment was repeated several times for different cooking times and temperatures between 62 and below 68°C, but the results were more or less the same. How could this happen? Why didn’t we get the expected perfectly cooked eggs according to the literature? Our yolks had become solid already at 65°C, while the whites were still not properly set, which seemed to be very different from what we had read about in the book. We searched scientific and popular scientific literature to find a straight explanation, but in vain. After all, most people cook their eggs in boiling water, close to 100°C. Could it be that no one had actually tried cooking eggs at other temperatures? Or maybe someone had, but hadn’t been among those writing research reports or cookbooks about it?

  The physicists’ eggs. When cooking eggs, the traditional way, at around 100°C, we rely on the laws of physics. The water is boiling hot, the egg is cold and the heat would expectedly spread from the outside in. Since all parts of the egg coagulate well below this temperature, the egg will solidify from the outside in. The white will become solid before the yolk is heated enough to become firm, and the higher the temperature, the firmer the texture. With this tactic, your best tool for a successful result is a timer. If you want to be very accurate, add a tape measure. Because larger egg means longer cooking time. This way of cooking eggs inspires physicists, in their spare time, to create complicated ma
thematical formulas for egg cooking, in turn ending up as egg cooking calculators on the web. Advanced versions take into consideration the desired outcome (soft, medium, hard yolk), the size of the egg, starting temperature of the egg (did you take it straight from the fridge or was it kept in room temperature?) and even elevation above sea level. The starting temperature of the egg makes a difference; if you start with a room-temperature egg, it will be as much as 16–20°C warmer than taken straight from the fridge, and, not surprisingly, this will require longer cooking times. The Norwegian egg cooking calculator tells us that taking a medium-sized egg straight from the fridge requires about 40 seconds longer cooking time compared with one kept at room temperature when you want it cooked to medium soft yolk. But why does the calculator include elevation above sea level? The boiling point of water depends on the surrounding air pressure, which changes with elevation, in turn affecting the cooking time. High up in the mountains at 2000 meters, water boils at just below 98°C. For a small-to-medium-sized egg this amounts to 30 seconds difference in cooking time for a medium-soft yolk. Such calculators, or equations, assume that you drop the egg straight into boiling water. If you start with tap water, pop in the egg and then turn on the heat, the calculator does not work because the water temperature will be constantly changing the first minutes. Making a functioning equation or calculator for cooking the egg from cold water at home would be a virtually impossible task because of the many factors that come into play in different kitchens around the world: the size and material of the pan, the amount of water, the type of hotplate and so forth. It seems that the world has not yet seen such a passionate soft-boiled-egg-loving physicist as such an equation and calculator has not been developed thus far.

  Cooking eggs in cooling water. Some rely on a trick that they claim will ensure a good result every time: heat water to the boil, pop in the eggs, take the pan off the hotplate and leave for a certain amount of time. As a general principle, this is actually a very old cooking technique described elsewhere in the book, dating back to prehistoric times: the cooking pit. In this case, hot rocks are used instead of water. This way of cooking the eggs relies on the ability of water to store the energy it receives from the hotplate, and subsequently to give it away as thermal energy to the food. The longer the food is cooked, the cooler the water becomes, so the risk of overcooking the eggs is not as high as when keeping the eggs at constant boiling temperature of 100°C. The same principle is also evidenced when cooking porridge, where the milk and rice is heated to the boil, wrapped in newspapers or a duvet and left to cook by the residual heat for a few hours. However, inherent in this method are some major pitfalls as the end results are very dependent on how much heat is stored in the system: do you have one liter of water or 10 liters? What material is the pan made of? Is there heat stored in your conventional cast iron hotplate, or maybe you use a convection hotplate of ceramic material that doesn’t store that much energy? If you heat one liter of water to 100°C, pop in an egg, and leave it for 15 minutes, you will most likely get a very different result compared with heating 100 liters of water to the same temperature still cooking one egg. One hundred liters of water will stay at a higher temperature for a longer time than one liter. And popping one egg into one liter of water should give a rather different result than cooking five at a time, because the five eggs will cool the water more than one egg, and they will have to “share the energy” from the same amount of hot water as compared to the single egg. Add to this, cooking eggs where the margins between undercooked, perfect and overcooked are narrow. The only way to assess the state of matters is to crack the egg open: the ultimate point of no return. So, if a cookbook was to give a recipe for cooking eggs in cooling water, it has to specify not only temperatures and time, but, at the least, also the amount of water per egg. But for your own kitchen, when you use the same procedure, the same amount of water and number of eggs every time, it might work out perfectly fine every time. You might even achieve some credibility among friends and family for being able to cook perfect eggs, according to your taste, in a very consistent manner. But it might be risky to share your procedure with others unless you give fairly detailed instructions.

  Cooking eggs at 6X°C - relying on chemistry. So, what happened with the eggs? What was the reason for our “Eureka!” moment turning into a typical “What the…?” moment even though we had been very careful controlling the temperature? The answer did not arrive until 2011, in a scientific paper by César Vega and Ruben Mercadé-Prieto called “Culinary Biophysics: on the Nature of the 6X°C Egg.” Our inside-out-cooked eggs had now got a name of their own: the 6X°C egg. The experiment that the two researchers did was quite simple, and very clever. They heated a large number of 18g samples of egg yolk to respective temperatures between 60 and 66°C for different lengths of time. Then they measured the viscosity, how soft or hard the yolk had become, for each combination of time and temperature. What they found was that the texture of the yolk was not only a question of temperature, but also of time, even at stable, low temperatures. In their research paper, the two authors presented this in a graph showing how the texture developed at various temperatures (see diagram). At last, these strangely cooked eggs had been described by science, or at least vital information—a missing piece of the puzzle–for us to understand how eggs behave had eventually surfaced.

  The viscosities, or textures, of the yolks were given as numerical values with the unit Pa·S. The researchers must have wished that their results should not be relevant only to the research community in soft matter physics and the like, but also for the rest of us. As a thoughtful gesture, they included a table where they linked viscosity values with familiar foods. After all, you wouldn’t ask the waiter that you would “like to have your egg cooked to 12 Pa·s at 10 s-1.” On the other hand, asking for the yolk to have similar texture as mayonnaise would give meaning to most people. Reading off the graph, a texture similar to mayonnaise would require cooking the eggs in 64°C for ca. 15 minutes, 63°C for 40 minutes, or 62°C for 75–80 minutes.

  Effect of cooking time and temperature on the structure of the yolk

  ^ During cooking, the structure of the yolk depends on both time and temperature. Pa·S is a numerical unit for viscosity. The higher the value, the more viscous (thicker) the yolk. The illustration is based on the original diagram by Vega and Mercadé-Prieto (2011)

  Viscosity of selected foods (adapted from Vega and Mercadé-Prieto, 2011) Food

  Viscosity (Pa·s)

  Whipping cream

  0.02

  Raw egg yolk

  0.09

  Pancake syrup

  0.96

  Chocolate syrup

  1.4

  Sour cream (17% fat)

  2.9

  Greek-style yogurt

  3.0

  Molasses

  3.3

  Sweetened condensed milk

  6.8

  Mayonnaise

  12.1

  Ready-to-eat chocolate pudding

  13.8

  Honey (liquid honey)

  18.3

  Nutella®

  28.1

  Cookie icing (fresh)

  29.3

  Toothpaste

  43.8

  Marmite®

  43.9

  ^ The table shows viscosity of various foods. High value signifies high viscosity. The table is adapted from Vega and Mercadé-Prieto (2011).

  The question, however, remains: Is there any point in making things more intricate than they are? After all, you might say that your Sunday egg comes out satisfactorily almost every time, that this is good enough for you, and that you would rather spend your energy on the Sunday newspaper. There are indeed reasons to try it at least once. For one, the texture of a 6X°C egg is quite different than what you can ever get by cooking the egg at 100°C. It is difficult to explain in a few words, so you just have to try it. Secondly, maybe we can return this question with another question: why put robots on Mars? Why should cur
iosity to inquire be limited to space scientists, rocket engineers, and the like? Space research is often justified by the fact that many inventions come out of work that was never meant to produce that specific invention. In the case of the 6X°C egg, this happened almost instantaneously. As soon as this way of cooking eggs became known, creative chefs started inventing new dishes, bringing our thoughts to a quote from the famous French gastronome Jean Anthelme Brillat-Savarin (1755–1826): “The discovery of a new dish does more for the happiness of the human race than the discovery of a star.” Brillat-Savarin is also the writer famous for saying, “Tell me what you eat, and I will tell you who you are.” It is worth reflecting upon that in the seven-year period in human history, between 2004 and 2011 while we could boast about our ability to put a functioning remote-controlled vehicle on Mars, we didn’t have the scientific knowledge of what goes on inside the millions of eggs cooked in kitchens around the world every day. On the other hand, maybe there was a chef, a housewife, or someone else loving their Sunday egg that knew about the 6X°C egg phenomenon all this time without sharing it with the rest of us through research journals or cookbooks?